Not sure if you would want to practice with a reinboard. Easy to make, can use it watching TV or bicycle videos going on roads and trails. You can go from two-handed to one-handed as hands get tired, practice with the whip touches.
Some thin cord, a couple pullies that fit the cord and a pair of regular riding reins, correct (for your hands) width reins. Perhaps reins with leather grips spaced out, will help you hold things better. Two little water bottles with screw on lids and a chair with a horizontal back rest. Hang the pullies on the rail of chair as wide as reins of horse/pony come into your hands. Cut two pieces of same length cord, which should be slightly longer than from pullies to the floor. Make a loop in one end of each cord so one rein loop can be attached to each cord. Thread the skinny end of cord thru the pulley, end going out the back of chair. Poke a hole in lid of water bottle, push cord end thru top of hole and knot the cord end on the threaded side of cap. Repeat with the other cord and water bottle cap. Then put an equal amount of water in both bottles, screw the lids on bottles. For safety, you may want to add a wrap of duct tape to prevent lid coming off the bottle should your handling of “fractious” animal require some creative rein work!
This rein board model works quite well with minimal investment, ready to use in any weather. A whip (dressage) should allow you to “touch up” a non-responsive chair on both sides without wiping out any decorative items nearby. Practice making loops, giving with the outside rein instead of pulling the inside during turns. You can do wrist rolls, giving and taking rein without changing your handgrip, reining straight back with both reins even. Keeping the bottles even, moving smoothly with the rein is your goal. Maybe equal spaced, horizontal colored tape lines will help spot slight differences in rein give or take with the bottle, easier for you. Electric tape comes in colors, is pretty sticky to make lines with.
Reinboard might help strengthen hands a little with regular practice between lessons. RMJacobs you might be able to make videos while riding your bike, doing up and downhill, tight turns in both directions, traffic, for days when you can’t get outside.