I've also been on those Air Dolomiti turboprop flights - I thought it was a great close-up view of the Alps. They've recently added a bunch of EMB-195s but not on that route.

If the objective is to stay off RJs/turboprops then another option to consider is to connect LH from FRA into BLQ (Bologna) - they do fly mainline jets into there. From Bologna it's about 1 hour by train into Florence. Might be less of a hassle than going through FCO.