If you're happy using film, IMHO, you should hold off as long as possible before going to digital. The longer you wait, the better the resolution will be when you jump in - and as an added benefit you'll avoid the constant "need" to upgrade.
Generally speaking, based on my experience, you still get better resolution from film compared to most digital sensors, particularly if you're using a Leica system (or medium, or larger, format for that matter).