If you insist on getting paddles, then get the smallest ones you can find. Tendinitis in your shoulders is no fun, trust me, and takes forever to heal properly. You probably do not have ideal technique, and so are more likely to hurt yourself with a set of large paddles. Throw away the wrist strap, just use a single loop over your middle finger. That way, if you have poor hand position or don't extend your hand past your hips, the paddle will rip itself off.
I am distinctly opposed to fins, I don't think they serve any meaningful purpose.
If you are looking for fun, there are a few options. Mix up your strokes more, join a masters squad, or get the "workouts in a binder" and follow those. Do something silly and challenging every once in a while, like a 4 x 400 set in IM order. (400 fly, 400 back, 400 breast, 400 free). The worst thing you can do is do the same workouts day in and day out. create a "workout hat", whatever you pull from the hat that day is your main set.
Swimming Workout of the Day: Favourite Swim Sets: 2020 National Masters Champion - M50-54 - 50m Butterfly