If you don't want to go to a gooseneck, you're somewhat limited in your options.
I've used a few tag along options that worked:
1) 5 bale mover with individual cradles. In my mind, the least desirable option. When you release the cradles, you have to lift the bale a bit by hand to get the cradle to overcentre and dump. With soft core bales in the 1500 lb range, its not bad, but with 2000lb hard core bales, you've got a sore back/legs by the end of the day. Plus, you're forever on the road. There are tandem axle 7 bale movers available. One of these would be better.
2) tag-along flat deck. With your receiver hitch requirement, you're not going to want to get too big. Maybe 18 foot. Loaded farmer style, you'll be able to haul 8 to a load. Good hard bales will net you 16,000 lbs to a load. Thats alot to ask of a tagalong, so you'll want a load equalizer hitch. If you load tube style, you could step to 20 foot trailer and get 12 to a load, 24,000 lbs. Thats a pile of weight for a tagalong. This will be your best option for hauling long distance.
3) Tri-haul mover. Add this to your flat deck to allow for auto unloads in the hay yard. Not going to save you much time when hauling from 50 miles away, but when hauling from within 3 or 4 miles, the auto unload will double the number of bales you can haul in a day.
Rod