Hi there
As a vet and long term lamber, I have seen a number of crosses to try and get the right size lambs.
As folks say, it is mostly the ewe and the feeding that determines singles/multiples, and it really will be conformation of the lambs that will help them lamb easier out of first-timers than anything else.
I knew one farm that lambed hoggs at a year old, these were texel cross ewes, and they were put to a Beulah tup, I've not seen many of these around, but I don't think we pulled a single lamb out of the hoggs that year, and they were all up and suckling like billy-oh!
Another farm I've worked on for 17 years uses British Milksheep and Lleyn tups on his gimmers (2 year olds as first time lambers) and the lambs generally pop out pretty easily also and are pretty nice lambs.
He often keeps some of these for breeding, and in their second and subsequent lambings they get suffolk or texel tups to cover them.
The Lleyns and milksheep tend to be prolific, so if you were looking to aim for more twins/triplets than singles, then if you kept some of these crosses they would likely do that for you.
Looks like you've got a lot of choices now, hope you find something that suits you

Suzanne