As you know, you want something that is a bit acid, but not hugely acid, but the plant isn't hugely fussy about it. So it makes sense to mix some normal potting compost with some ericaceous, some sharp sand, perhaps a bit of grit, and if you have some throw in some some perlite or vermiculite for good luck and improved texture. But if I only had normal compost to hand, well I'd use perlite (its more acid than vermiculite) and ericaceous fertiliser. And if I had some ericaceous to use up, well then I'd use vermiculite and normal fertiliser. But then I keep both of these in my shed as I use them regularly for potting.