If anyone can solve your challenge, not settle and look until you find the absolute perfect solution, it's you Angie! There are a lot of great ideas here. I didn't read them all, so forgive me if I'm repeating someone's idea.
I think all of Inge's mitten ideas are super cute!!! What if you add liners inside them? A., they'll take up some extra room, B., Your hands will be covered enough even when you need to take said mittens off, C. layering adds another layer of insulation, so they'll be much warmer.
I have used polypropylene glove liners with great success. They're not pretty, but then they're not for looks. (Being the material of long underwear, you'll find them in the gear stores, like REI.) They're fairly thin, so you still have a bit of dexterity when you need to attend to Sam, get a credit card out, etc.
Another solution--I totally echo La Pedestrienne, Hestra!!! I have been a skier for many years and for most of those years, I suffered with cold hands, even with the glove liners. I was thrilled beyond measure when I found Hestra--they're truly amazing!!
Oh my! I just found these, https://www.rei.com/product/13.....ens-womens. Yes, they're gear (but sometimes function wins over fashion, esp in cold weather.) And I just read in the specs that they're slim with removable liners...and they're part white, so there's another plus.
Hope this helps...best of luck to you!!