I agree with Iddee, don't think small when it comes to hive sizes. There are folks that keep bees on balconies so I am betting your yard is big enough for a couple of hives close together.
If weight is the concern, 8 frame might be something you look at, or run all mediums. If you are trying to limit colony size, swarming is going to cause a bigger problem for you.
Oh, and Welcome to the forum.
