First off, if you want some income from fleece, take great care to buy stock with excellent fleece. That might sound obvious, but there is a huge variation in fleeces, and spinners, felters and other crafters will only be interested in the very best. Depending on the breed you eventually choose, I or others on here may be able to point you at someone who has sheep with excellent fleece.
Even with sheep that genetically should produce good fleece, many, many factors can cause a fleece, or an entire clip, to be of no interest to crafters - whatever the breed of sheep. Some breeds are particularly prone to the fleece being unusable when harvested.
Much of this next bit is received knowledge; I have personal experience with a very small number of some primitives (6 Castlemilk Moorits, 2 Manx Loaghtans and their Shetland x offspring, 4 Shetlands and several Shetland crosses) over the last 3-4 years, but read (and seek out and watch and listen) avidly about other people's experiences.
Soays are the tiniest of all the native primitives. Very easy to look after (provided the fences are good and they have plenty to eat / no reason to want to escape

- which is true of most of the primitive breeds), great feet, super meat (but not very much of it on each carcase.)
Soay fleece is interesting to spinners because it is rare, but it is not actually very nice for spinning. It is rare because it is very difficult to harvest - Soays, even more than other primitive breeds, are 'self-rooing', and shed their fleece in patches. So you would either need to 'glean' the bits of wool they leave on fences and plants, or would need the sheep to be so tame you can catch them every week or so in May and June and pull off whatever is ready to come at that point.
Next in size and also interesting because very rare is the Boreray. This is a breed that needs a lot of help; it's the most endangered native breed. It's not a novice spin, and some of the fleeces are frankly horrible. However, because it is so very rare, and is double-coated, and is multi-coloured, then you would find buyers for fleece if you manage to get good quality fleece off your sheep. However, being a double-coated fleece, the fleece can get ruined while still on the sheep's back.
Similar, slightly larger, and used to seaside living

, is the North Ronaldsay. This is the one that is famous for living on seaweed. There is a flock in Northumberland which are super sheep with lovely fleece, and are used to more copper in their environment than the island sheep could handle, should you decide on these. These are also double-coated, but nice fleeces will have spinners queuing up.
Hebrideans seem to be very easy to look after, a decent carcase, and nice Heb fleeces are a joy. However, all spinners have been offered really horrible Heb fleeces - it's another breed whose fleece is very prone to felting - so you may not find it easy to find buyers for your fleeces. Others on here know
way more than I will ever do about Hebs and their fleeces, so I won't write more about them.
Manx Loaghtan are intelligent and wily, and a nice Manx fleece is total luxury, IMO. My own two are very inclined to self-roo in patches, so it is not always easy to get a nice fleece off them, however. My one Manx is the most escapey of all my sheep - she doesn't regard it as escaping, she just comes to find me when she needs something

Castlemilk Moorit are elegant sheep, slightly larger than the foregoing, and a really nice CM fleece is wonderful, though not appealing to all. I only know two breeders who have really excellent fleeces, however

. All the primitives have really tasty meat, and CM is quite distinctive. It's lean and almost gamey - most people really love it, even if they generally do not like lamb. My own CMs have been friendly sheep, not hard to look after. Less inclined to go walkabout than some other primitives

I got 55kgs butchered meat off 4 3-year old wethers.
Shetlands are smaller than the CM, but have the benefit of being readily available and coming in many different colours (very appealing to crafters.) Again, not all Shetland fleeces are nice, and some nice ones aren't usable (some have a 'break', or weak spot, in the fibres, which makes them useless), but good ones are superb.
Portlands are from way further south, and hard to find up here, but there is a flock in the Borders. Nice Portland fleece is very nice - but not all Portlands have nice fleece (are you seeing a pattern here?!) The meat is delicious. If you can get sheep with nice fleeces, you would find buyers for them, as there are not many available this far north. Portlands have been used for conservation grazing on Braunton Burrows in North Devon, and did a good job, requiring very little intervention / maintenance.
You could also consider crossbreeds. If you cross a Shetland with anything larger, you get a much larger sheep than the Shetland, but often retain most of the good characteristics of the Shetland. I have some Blue-faced Leicester cross Shetlands, and one which is 1/4 Blue-faced Leicester, and they are excellent sheep, producing decent fat lambs and a superb fleece.
I have also crossed my Manxes, and been very pleased with the progeny. There seems to be lots of hybrid vigour in a Manx cross - they've been larger than their parentage would have led you to expect. They retain the Manx' wiliness, though

And walls are just vertical paths...

Get yourself to Woolfest at Cockermouth Fri 26th June / Sat 27th June, and have a look at some of these breeds, talk to some owners, and see what appeals. I don't think all the breeds I've listed will be there, but some will.