Lindemann Engineering affordably rebuids stock struts and claims good results. I contemplated them when I was replacing the tired struts on my old R1100RT but got the urge for new ones and put on a set of Hyperpros which I liked. Any new (or rebuilt) shock will be amazing if you've 30,000 or more miles on your old one. You might consider replacing the front too, though you'll probably notice the rear most. You might be able to confirm the diagnosis by visually inspecting the point where the shaft enters the tube while the bike is being bounced by your heaviest available assistant (or reverse roles). In addition to poor handling of worn shocks, if there's still a lot of oil in the shock and the seals fail more completely, you could dump a nice puddle of oil into your rear tire's path.
At this time last year Bob's (Ohlins dealer) had a reasonably good sale price on their Ohlins TTX shocks, which seemed a good idea for my R1200GS. I was in a mood to support my local dealer and gave Mattigan good information about the riding I do, weight, etc. and placed the order. I installed them myself and was amazed the sag settings were spot on without adjustment. I haven't messed with them much since, other than to slightly dial back compression and rebound damping front and rear. One of theses day's I'll try decreasing the damping a lot and increasing spring preload to see if I can turn the bike into an off road pogo stick. But on gravel, forest service roads, etc., they work great as is.
On your bike, the rear shock is super easy to do. The front is easy too, once you get past the body work and fuel tank.
You could hunt some and maybe find a group buy on ADVrider or somewhere.
NJ-based R1200R rider and frequent SRR attendee Don Eilenberger has a nice writeup on suspension setup
here. Required reading.