I've had a backrest on all the bikes I've owned. The Goldwing would be no exception. When I was looking for a Goldwing I decided I wanted to use a Utopia backrest.
I ordered one from HDL. It was well-packaged.
Here is the kit. It comes with nice instructions.
The next step makes some people a little squeamish. Mark the seat per the instructions, stick on the hole protector, then cut a 1 1/2" slice in the seat. The goal is to cut through the seat foam down to the holes you drilled earlier. If you lay the seat on its side you can see the angle to cut through.
I started with a 6" knife but had to upgrade to an 8" one, and it was almost too short. Here you can see the tip of the knife blade at the first hole. Work the knife up/down and back/forth until you create a large enough 'path' for the intermediate brace.
Insert the intermediate brace and work it through the cushion until it lines up with the holes you drilled.
Bolt the bottom and intermediate brackets together.
Attach the backrest. It has several means of adjustment.
The backrest includes a zippered rear pouch. A nice touch.
The backrest folds over for easy access.
A nice, comfortable setup.