You could try a Charollais. They're big sheep but the lambs are born small, slippery and very lively, eat well and grow well, and are very solid, so always weigh more than their Texel or Beltex peers of the same size. It's beautiful, succulent, sweet-tasting lamb, too.

I don't have personal knowledge of the Charollais on BFW but I can tell you that the Shetland Sheep Society at ScotSheep last week was promoting Beltex crosses on Shetlands and Charollais crosses on Shetlands.
Charollais should produce cracking fat lambs on your Suffolk and Wilts Horn ewes.
The only proviso I would give about using a Charollais tup is that if you get much in the way of cold wet weather at lambing time where you are, make sure you get a tup with plenty of wool on his face and head. Otherwise you can get lambs which are really quite bare at birth, and they can't take a lot of cold wet weather if they're bare. (The plastic lammacs work fine, though.)