Are you likely to keep any of the resulting ewe lambs for breeders? If so, that might affect your choice of tup breed.
Whereabouts are you? If in t'South of England, Charollais would be fine. If somewhere colder/wetter, and lambing outdoors, choose a Charollais tup with wool on his head; the very bare tups beget very bare lambs, and if they're born outside on a cold wet night, they may not make it. (Although they are very active lambs, and usually get around to the milk bar very promptly.)
Lleyn would be easy lambing, I'd think, as they have less backside than most breeds. If you would be keeping females, I'll add that as replacement ewes, I only have one criticism of Lleyn crosses, and that's that they have too many lambs. But if you're somewhere warm with good grass, I'm told that's not an issue as they can rear three on good grass. They don't work well hereabouts, our ground's not good enough to rear three on grass, Lleyn or not.
For lambing Texel type hoggs, I would say that the most important thing is lamb vigour. You need lambs that will jump up and find the milk bar, no matter how silly the mother is being.
To which end, my two recommendations are Charollais and Shetland.
Shetland cross lambs grow well, and are very saleable. The females are good breeding sheep, and the males will sell well as late season lambs, or as stores, because they'll likely be white and look more-or-less like Texels.