Same concerns here! We're off to Borovets on 9 Feb, and particularly booked into the Hotel Victoria which mentions catering for vegetarians in something we read. Am keeping my fingers crossed, and thinking that if worse comes to worse, it won't hurt for me to lose a few pounds!
Good idea about taking some marmite - I have some mini-pots lurking in a cupboard somewhere. And nuts/raisins/chocolate will always prevent starvation!