Just a quick update. I tried a pair of small mens last night and the pad itself was a nice fit but the middle strap was far too short and didn't reach the buckle.
Afterwards I had a bowling machine session where I tried some different stances and found standing 2-3 inches more to the leg-side eradicated this issue. I like to bat very side-on but did try a more open stance (which is what a lot of modern coaches suggest) but it just doesn't work for me as I then tend to get squared up. Side-on minimises my movements, I simply go forward or back. What was quite fun last night was setting up the machine to bowl slow but awkwardly straight pies then working on a few shots how to cash in on such filth. I may in future get caught or occasionally stumped but hopefully, I have eradicated being LBW (regardless of whether I've hit it or not).