You SHOULD be okay with just fresh soil. BTW promix has lime in it, but it is measured at the factory to give a predictable pH and it's appropriate to a peat-based potting mix.

There is a thread in the FAQs called why I shoudl re-pot and a sticky in basic about a continuous canopy- you should read those. Re-potting should always be to a SLIGHTLY larger pot, especially in a peat mix. It's all explained.