I know of 2 specialist agencies: Ski Solutions and Alpine Answers. If you tell them what your criteria are they will make suggestions. I have used both and they are both good. However they aim at the mid-market upwards (neither "do" Bulgaria) so may not be what you're looking for....
Borovets staying at the Rila, which is right on the slopes. Food is ok (for Bulgaria) Massive breakfast buffet with hot choices. Dinner is less good, but eating out is cheap so B&B might be a better option.
Main operators are Balkan, Neilson and Crystal. All seem to use the same Thomas cook flights, so the only difference is price. Rila has double rooms, and also has studio rooms which sleep 4, but both have access to the same facilities.
The full ski pack - lift pass, ski & boot hire, lessons 6 x 4hrs - is the best value. The instructors at the intermediate level really act as guides, and take you to the best places for lunch .
Not been to the other big resort, Bansko, as you have to get a cable car to the slopes and I prefer ski in ski out.
Just someone who can help with all the detail- I find everywhere quotes different things and it is time consuming to work out all the constituent parts etc, I want someone who can say trip z to place a costs z trip y to place y costs ybetc. Going independently sounds fabulous but to be honest i don't know where to start ESP when looking at places like Bulgaria.....
What are you looking for? We always go independently, as do others on MN, while many prefer packages. Therefore you will get lots of opinions here. Not sure what the expectations are of a skiing travel broker!