The distances you're hitting are in the lower half of regular flex and certainly not out of place. I don't necessarily think you need to change. According to the GCA (Golf Clubmakers Association) flex chart, when your 9-iron carry's less than 100m you need to drop 1 flex.
The benefit you will gain from dropping to action/senior flex will be more noticible in the ball flight than distance. Distance comes from both club head speed and timing of the impact, not really from shaft flex. If you don't increase club head speed and increase the accuracy of your strike you won't gain distance. It is a myth that shafts with more flex automatically increases club head speed.
Straight off, without even talking about shaft flex, a 25-handicapper with or without a physical limitation shouldn't be hitting 4 and 5
irons. Get yourself hybrid 3, 4 and 5-irons. They are so much easier to hit than the equivalent
irons for a number of reasons but for you the added loft will get the ball in the air with greater ease and consistency.