2 tips which I heard about but have never tried.

I was told that freezing the bean/lentil dish after it's cooked will lessen the gas problem. If all else fails, there is always Beano

Also regarding garlic. I was told that what makes garlic indigestible to some people is the germ. To solve that problem cut the garlic clove in two and remove and discard the "heart" located at the center.