kelehedo:
First of all, welcome to the Forum and congratulations on selecting the R9.
I can relate to your problem, having lost a good part of the ring finger of my right (dominant) hand during some "unpleasantness" in another life, requiring a couple of reconstructive surgeries and some tissue grafting to repair the stub. (The thing still bothers me at times after all these years.) I would just take it "nice and easy" with the R9, perhaps firing a single magazine per range session until you have familiarity with the piece. If you ever need to use it in life threatening situation, I can practically guarantee that your adrenaline level will be so high that you won't notice any discomfort in your shooting hand -- at least until later. Meanwile, one of the Hogue sleeves you mention might be useful during range sessions. Several members around here use them. And you can always remove it if you think it adds too much bulk in carrying the pistol.
Again, welcome, and good luck to you!