Yeah, not cheap but look into the Pullrite SuperGlide hitch specifically designed for a very-shorty 5.5' bed. 12k max trailer weight, model # 3100. Fully automatic so you never have to worry about forgetting to slide the hitch.
The SuperGlide hitch is probably all you need, but if you still cannot make a 90° turn with that hitch, then you might also need an extended pinbox, such as the Reese Sidewinder.
And there is no law that says you have to be able to make a 90° turn. I plan to tow my 5er from Austin to Midland next week, with my F-150 that has a 6.5' bed, using an ordinary non-slider Reese hitch. However, rule 1 for that one-time trip will be to never
put the tranny in reverse when the 5er is tied on. And before we hit the road, practice in an empty parking lot to be sure I can turn as tight as the pickup will turn while going forward, without cab to trailer contact. With a 6.5' bed, most pickups cannot turn sharp enough to result in cab-to-trailer contact unless you are backing into a jackknife.
But with your 5.5' bed, practice in a big empty parking lot with a good loud-voiced spotter, so you'll know what you can and can't do with that trailer tied on. With the SuperGlde hitch, I'll bet you can back into a 90° jackknife. But maybe not 91°.