I was in your exact spot a year ago. I ended up getting a 16' toy hauler (no toys, I just like the large door) that is something like 3k+ lbs loaded with a weeks worth of stuff (the cabin is actually about 14'). It's small, but anything bigger and I think it would slow you down too much. If there is any sort of head wind you will slow down. I did 75 with it once behind a semi, just to see if I could (not recommended, at all...). Hills will also slow you down, a lot.
Things I recommend you get:
-85-140 or 75-140 gear oil
-brake controller, could be a cheap one, but get something so you can hit those brakes hard if you need to.
-Sway bar kit for the hitch so the trailer doesn't move you around so much. (I got mine from harbor freight, it works quite well.)
If you really want to, you could get an 18', if its all flat ground, with no wind, cold weather, and a 50mph speed limit. With my 16' in July in AZ, my coolant was a little hotter, but other than that, it did ok, slow, but ok.
Just remember to drive in 3 not D, accelerate and brake slow, keep an eye on your engine temp, and check you engine fluids periodically.
My wife and I looked at some 12' trailers, and they are just way too small...