when i did my big weight loss a few years a go, i bought the same suit 3 times and sold the bigger ones on ebay!!!!!!!
and i did the same with a pair of trousers, started as a size 26 from evans, in the end i bought a 16, and wore them till they hung off me (ive kept the as i love them)
i tended just to buy a couple of cheap bits from primark or the likes, as i have to look smart at work as well.
there is a big (no pun intended) market on ebay for larger clothes. i made a fortune and what i sold them for paid for the next lot.