I wouldn't. I doubt flowerbed mulch is anywhere near the same as packaged bark. I doubt it's sterile. I'd stick with your current mix unless you are somehow unhappy with it. I use coir and perlite, about 2/3-1/3. Nice thing about coir is you don't have to repot every year or so like you need to with regular potting soil. Though it may be a little bit more price-wise initially, it ends up saving you a lot of money (and, even better, time).

Denise in Omaha