When I started BJJ, I was probably like you.
I was trying to find a game that I could use effectively for my own body Spider Guard didn't work because I had to be very flexible and wasn't... Butterfly guard required a lot of leg dexterity to utilize hooks, grips that I just didn't have, De La Riva and the modern games was never a fit for me, I couldn't go upside down; the half-guard was the easiest game for my body - it required no special talents.
Now after 17 years doing BJJ, I can say that everything I won in this game was from mastering the the Half Guard; it is a simple game, that everyone can practice, especially the older grapplers, because all you have to do is to lock one of your opponents legs and use a system that works. Even if you aren't fast, strong or flexible, you can win from Half Guard.
If you already have my Half Guard Instructionals, I would suggest taking a look at Lucas Leite's DVD, because it is pretty similar to my single leg half-guard, but in a way that favors smaller guys - Lucas prefers fighting bigger guys!