What about speaking and writing? I'm not too familiar with this situation as at my school, we had to do either Higher for everything or Foundation for everything. As Lil said, I know you can get a B by mixing them up, but I think you'd probably have to do at least half of the exans as Higher, eg Higher reading and writing with Foundation listening and speaking or something like that. If you do coursework, you could probably get away with doing 2 Foundation and 1 Higher as long as you as you did well in the coursework. One question though; if you think you're capable of getting an A, why would you need to do Foundation for anything?