In The Power of Three and Pond Life Amy is seen in a pink dressing gown and pyjama set. These have not yet been ID'd, but as the design is quite common, it's pretty easy to find a good alt.
There's a few different shots but nothing we've seen gives us a lot of detail. I think in most appearances it's just a plain white, or blush, singlet (vest/tank.) However in the second Pond Life episode we can see lace detail on one strap, with another, plainer, strap. It would make sense that it have lace to match the robe, but as we don't see another angle, it's impossible to be sure exactly which top, or tops, she's wearing underneath.
The dressing gown is pale pink with vintage lace trim on the cuffs. It looks to me like it would be slightly stretchy - a cotton, viscose blend perhaps, the sort of thing you can pull tight. It's probably three-quarter length. It does not have a hood.