Well another idea is to start with some wether lambs of a breed you think you might like so you can see how it works out. They'll be to eat anyway (maybe after taking a fleece, depending on the breed and whether you want a fleece) so if you decide that breed's not for you, you can get a different one next time.
I suspect there will be Southdowns and Ryelands in Lincoln, both of which I hear people talk about as being good, meaty, docile sheep, good for smallholders and children. The Southdown would be smaller, I think. Neither of them is a rare breed, however - but looking at the RBST Watchlist, there doesn't seem to be anything on there that meets your spec, except maybe the Hill Radnor or the Dorset Down if they aren't too large for you.
Most breed society websites have a 'marketplace' or 'for sale/wanted' page, and would put you in touch with breeders in your area.
Good luck, have fun looking and choosing - and let us know how you get on, please!