First let me qualify that my experience is with North Country Mules out of Swaledale mothers; I am not sure how different a Scotch Mule (out of a Scottish Blackface mother) might be. Possibly she'd have thicker-set lambs, and perhaps she'd be more flightly and not quite such a good mum as the NC type, but that's hearsay not experience.
If the ewes haven't lambed before, then the problem is that the new mums will adore every lamb they find, whether or not it's their own. So best to have them handy and get them penned as they lamb, while they bond. Generally they love their lambs and let them feed without too much hassle, so the only real issue is the mixups. Experienced ewes are much wiser and better at not accidentally adopting lambs that aren't their own.
So if they're first-timers and you'll have them handy, and penned for a day or so, then I'd use a Charollais. Easy lambing, land on their feet heading for the milk bar. Can be rather bare, hence, especially if it's cold and wet where you are, you'd want them handy / indoors.
If Charollais not suitable, we've been very pleased with our Dutch Texel on first-timers - a little smaller than regular Texels, tight skins (so slip out well), nice active little lambs that grow on well.
If you have to use a Texel on first-timers, try to get a one with less massive shoulders.
I've never used a Suffolk myself, so can't comment about that, except to say that we did buy a pen of scotch-type Mule hoggs with Suffolk lambs at foot - and they were pulled right down by producing and rearing those twins.
Looking forwards to pregnancy and lambing, it would be best if you can get them scanned and have at least the triplet carriers handy so you can help any with problems; also if you had any single-bearers, you'd want to feed less or the lamb may become too large to lamb. If you can't scan, then I would advise that you avoid flushing so hope for no or few triplets, feed well in the last 8 weeks of pregnancy on the assumption they're all carrying twins.