I was at the mall doing some "research" on petite-friendly parkas (per so many of your requests!) and got distracted by a rack of these heavenly soft tees. The lower-priced regular version is very cozy, like a cross between a regular tee and a lightweight sweater ("carlton grey" is lovely in-person!). The material of the olive green one I got is slightly different and labeled "plush" with a more fleeced feel, and there's a marled grey version too. These tees have a slouchy casual cut, with a back long enough to cover the bum, so I've been wearing mine with leggings, jeans, and even to sleep in! The only issue is the neckline of an xs is borderline low on me, so perhaps try sizing down - I didn't realize they come in xxs online and also in new petites sizing which should fit better!
On the winter coat front, several of the ones I've tried on fit pretty well, despite being in regular sizing and not petites. I stumbled across this faux fur hooded parka in xxs which was a return at Express, and after trying it on I could see why - I could barely zip it up with just a tee on underneath! That size would be perfect for extra slender ladies. The coat was surprisingly thick and well-proportioned for petites with a higher nipped-in waist, so I'd definitely recommend it as an affordable option. Just size up if you want to be able to layer. Sale items there are currently an extra 50% off right now, with free shipping on all orders!
At Macy's, coats are all on major sale (at least half off!) but as a result the in-store selection was a cluster. Favorites out of what I tried on were this Laundry by Shelli Segal puffer & this Lauren Ralph Lauren puffer. They were both only a tad big on me in regular XS and could be fine with layering underneath. Note the faux shearling lining on the Lauren coat is just along the button placket, not throughout. That one also comes in petites online (pxs should be perfect for someone my size) but with very limited stock left. Another puffer coat available in petties and still left in several colors/sizes (with faux fur trim listed as removable) is this affordable Kenneth Cole option, but I wasn't able to find it in-store to try.
We're headed somewhere frigid for the weekend, so for those who asked for warm winter outfit ideas, stay tuned! And here's a few more photos of this tee tucked vs untucked, as well as worn normally vs. shrugged off the shoulder for a slightly different look.