Southdown?
The easier-lambing Texel, in our experience, is the Dutch Texel. We paid £450 for a very good DT tup a couple of years ago; there should be more available now.
I'd have thought you would sell Lleyn x Texel or Dutch Texel as breeders no problem. Everyone knows the Lleyn is a good mum, very milky, easy lambing, pretty too!, but a bit too prolific - which shortcoming the Texel could tone down

Texel fleece is nice, DT even more so

. Charollais is better, mind

Exmoor Horn is a hill sheep so I wouldn't have called it a terminal sire, and the fleece is on the coarse side, certainly compared to Down breeds, Texel or Suffolk. You could use it to add hardiness and weatherproof fleece then add Charollais in the next generation...

Romney would be a very interesting cross. Should be nice fleece too.

I don't know how you would fare selling fat lambs though. Lleyn x Romney ewes... I'd think about buying some! (If you were in Scotland!)