Re-pot blueberry?

Well, I've had my blueberries for a couple of years now and fingers crossed, they are starting to get established.  My favourite is the Chandler, as it has those really big berries  but it is now over 5" high  and I'm thinking it may be due a 'promotion' to a larger pot.

So, my first question is, if I re-pot it now, will it affect this years fruiting as it tries to re-establish itself?  If so, I shall wait until it's fruited first. 

My second question is, if I do re-pot it, should I use 100% ericaceous compost or should I mix it with anything?

Mags

Thanks Trillium, new pot coming up.