How to Combine a Retnoid and BHA?

Dear Sir/Madam, How can I combine a Retnoid creme and BHA in my routine without causing irritation? Before I started my second course I used Tretnoin 0,05 creme (PM) and 2% BHA gel (AM), but this was probably a bit too much. I got flaky through out the day. My skin will probably be not as oily in the t-zone after accutane. Unfortunately 0,025% Tretinoin is not available in Germany, I thought I could switch to Differin 0,03% to avoid dryness. Can you recommand that? How often should sb. with exfol.