Best bedding to use? possible allergy

Hi
Ive been putting hay in with my mice and using shaving of different sorts, lemon scented/lavender from pets at home
Some of my mice seem to be wheezing and there eyes seem to be a bit stuck shut when they first wake up, one of my mice is about to go to the vets for some baytril

Is there anything I can use for bedding which is just plain and simple, wont cause them to be allergic or anything??