Having not skiied in over 5 years on snow, would you recommend either - buying a set of ski boots in the UK, hiring them on Borovets or buying them in borovets?
My view is that if you intend to ski every year and given that ski boots can make or break your ski holiday, I would invest in your own boots that you can get custom moulded to the shape of your foot to ensure maximum comfort. At least then you can have the bindings on any ski's adjusted to fit your boots, ensuring you a comfortable days skiing.
Personally, I would buy in the UK and have them adjusted and moulded in the UK so that by the time you get to Borovets you won't have to worry about wasting valuable skiing time walking around the shops trying on loads of boots and getting the adjusted etc.
Can I suggest a professional boot fitting company called Profeet. They are te best in the business.
I was in Borovets this year along with 16 other people in the group. Two of us went over there with our own skis and boots and twelve came back with skis and boots.. There are plenty of ski shops over there so you can barter with the price.. One of the group contacted his wife who did not ski for price comparisons back home on the net and for the same skis and boots, they were consierably cheaper in Borovtes for the same models etc.. Buy over there...