I would use fleece for her to lie on (in fact, I bought one for Dumbo when he was going to Karen but decided last night to give it to Floppy as a present, if you want it?).
Actually, something else that might be even better would be vet bed (which I believe you can get from P@H) because when she wees it will soak through.
The risk with her being in a carrier is that you have to move her out to change it, which will be unsettling and painful. I wonder if having a small space, that you can effectively change around her might be better for her. Like a triangle made from your puppy pen sides, or maybe a small space made with NIC grids (have some I can lend you if you want)-that in itself could go inside the puppy pen, which is presumably where Harley will be living?
Whatever you give her to live on and wherever she lives she is going to need to be cleaned out several times a day to avoid her sitting on anything that could irritate her.
To keep her cool its no different from the other buns really, same as with heat, just as long as she can get away from whatever you give her then it should be fine.
We already know she plucks her fur when she is distressed/unhappy, so that is going to be one to keep a close eye on.
I know you want to do this right, but remember there is not really a right now wrong, it's just working out what is best for Floppy, and that may change, and its also about doing the best you can with the info you have at the time, which is what you are doing, and you're doing an ace job
