jen - i just have the bassinette matress and a sheet over that, and then i fold a cloth nappy in half and put it where his head is, good for if he spews or something, dont have to change the sheet! they did it in the hospital and it looked like a great idea lol!
if the matress seems uncomfortable maybe put a sheepskin under the sheet? hmm yer that might be uncomfortable for her, depends how much higher her legs are.. the matress in my basinette doesnt seem very comfortable, its just kinda a plastic thing, cant really explain it but yer he seems to like it!