As has already been said, there are a ton of variables here. At 5 years, a Sulcata can range anywhere from 10 lbs to 60, depending on how it was raised. A Sulcata raised in inappropriate conditions will, naturally, grow slowly. If cared for correctly, however, meaning fed an appropriate diet, kept warm, humid, and hydrated, with enough space and appropriate UVB, they can grow FAST. Maybe not so fast that you couldn't still house him in your current yard until the move, but fast enough that space may be a concern by the time you do move to a home with a more appropriate yard.
Another thing to consider is the winters in your area. It is plenty possible to keep a Sulcata in this environment, with enough dedication and large enough "indoor" accommodations (i.e. a converted basement or a large heated shed), but it is also very difficult. For this reason alone, unless you're prepared for the effort and expense that will go with preparing appropriate winter accommodations, a smaller tortoise may be the better idea.
As far as my personal favorite "smaller" tortoises, I'm a big fan of Russians, which stay very small (5-8" being average adult size). They have a great personality, very hardy, and very easy to accommodate indoors. Other Testudo species, i.e. Greeks and Hermann's tortoises, are also great options.
As someone else suggested, Redfoots are a really fun one. Very personable and interactive tortoises. They do get pretty big, 10-14" max size if I remember correctly, but still manageable and not so big that it's difficult to house them indoors for the winter.
I'm a big fan of Leopard tortoises. The Babcocki subspecies stays small enough that housing one indoors during the winter isn't too far out of the realm of possibility, with their usual max size being 18". The downfall of Babcocki leos is that they tend to be a rather shy tortoise, not possessing that same great personality as a Sulcata. The Pardalis subspecies, on the other hand, gets bigger, closer in size to a Sulcata, usually has that same great personality, and tends to be much more cold tolerant (not a hibernating species by a long shot, but not as prone to illness if it gets chilly during the winters).
FWIW, my favorite tortoise info resource is
http://tortoiseforum.org. It's a forum, like this one, dedicated solely to tortoises. The people there are knowledgeable, friendly, and very helpful. Once you figure out which species you'd like to pursue, they'll be able to point you in the right direction as far as good care regiments and links to good care sheets/sites.
Wow, ended up writing a novel. Lol. :P Good luck with whatever you wind up doing.
