We didn't ever both with thermals, tbh. Just regular bodysuits and leggings. Even with the one born in the Canadian Rockies in January, lol. I think the youngest we bought thermals for was when they hit three and we started them actual skiing. Before that, they just wore regular sensible simple layers under their snow suits. We had a billion fleecy jumpers that we used as a mid layer. Just regular off the shelf fleece tops from whichever baby shop had them (and they all seemed to). Boden always did a killer range of fleece jumpers for babies. 
you really don't need specialist stuff that will be worn for a week and then discarded (and you know it will probably get vomit or pooh on it the first day and you'll be washing every night...) I suspect mine have even worn large babygro under their snow suit. You have to pull the babygro feet down though, as they can ride up and tighten when you slide them in - you don't want cold toes from them not having enough space to wiggle! (Has your snowsuit got feet in?)
I have always felt largely the same way about the back pack idea, but have never once fallen when carrying them - have seen total nutters downhill skiing with tots in backpacks, and am not that crazy! Daycare works for me!
Skiing is compatible with bf here. They take babies from 19 days old and give you a pager and just page you when the baby needs a feed. 
. It ain't all that sensible though, I put ds1 in for a day at 10 weeks, and he ended up with rsv and double pneumonia. daycare comes with preschoolers germs from all around the world lol. The same kid was hitting black runs at 7, though, so it didn't put him off!!
Mine wore sunglasses, not goggles, but it's very much what the tiny will tolerate, tbh. One of ours refused point blank, so we ended up putting a peaked cap on in between the warm hat and the snowsuit hood, just to shield the eyes a bit.
You will have sooooooo much fun! Have a lovely time!