Your Ranger will do OK with any of the trailers from the '50s and early '60s up to the 22' Safaris. A '53 Flying Cloud would be a good match at 21'. They were very lightweight in comparison to the current behemoths. If you buy one fully restored, you'll be paying about as much or more as for a new-out-of-the-box trailer of the same size. They can be found in useable condition for under $10k though. You'll also be ok with a late '70s Argosy Minuet 20'. They were narrower and lighter than the earlier Argosy 20s. Any trailers built after 1967
over 17' long will be too much trailer for you, particularly if you have a short wheelbase Ranger. Set it up with a Prodigy or P-3, and a Reese Dual Cam and while you may not set any land speed records, your rig will take you anywhere you want to go.
Over the years I've towed a couple of Flying Clouds with a Toyota extended cab Compact Truck 3.0l V-6, 4WD and auto and they were a good combination. I also towed a '61 Bambi with an '87 Toyota long bed 2WD 4cyl (20R) with an auto and a Minuet 20' with the '87 Toyota.
I also have had a number of fiberglass trailers in the 13-17' range that would work well with your Ranger. Just another option.