It isn’t just about disc brakes vs. rim brakes, newer bikes use a different spacing and through axles rather than quick release skewers. Most rim brake wheels use quick release, so they may not even fit your frame.
If you are not sure what wheels you need, you should ask a bike shop you trust. Getting a trainer wheel is generally a good idea. Usually people run a nice wheelset outdoors and a crappy one indoors. So you might want to consider getting something nicer for outdoors and use your current wheelset indoors.
It seems you might want to consider switching bike shops. There are plenty of good bike shops in Toronto, and depending on where you live, one of them might be close to you.