I just use cheap over the counter covers in the garage that you can get at most any auto store. They are too big and don't fit well but are great dust covers. Only thing I would make sure of is to get something breathable, not plastic, to avoid condensation problems.
Carcoverstore.com has them, good quality and reasonably priced. My friend who has young kids put a short aluminum fence around his car to divide the halves of the garage and to prevent bikes, kids. doors etc from damaging his ride.
Kids and bikes are a concern now that there is two in the garage. If fact, I seemed to get some anxiety having two now. I will see how that goes over the next few months. I have a good size garage but I have given up space, ease of use of the garage.
I use a cheap Budge 3 layer cover about $60 bucks. Feel like a thick paper towel. No dust under the cover over the winter. Universal fit is very good almost too good if you have a good wax job. Would protect against a kid rubbing on it. I doubt the best cover would protect against a bike hit