I'm not sure what information you're seeking, really - if its potbound currently, you'll need a pot about an inch larger all round, preferably using John Innes No. 2 or 3 for the compost, or a mix of that and a good multi purpose one.

I would do a tree/shrub/rose compost which has all the benefits of leaf woodland base without the higher ericaceous need. All firs grow in a slightly acid based soil, which is low in normal garden nutrients. Think leaf mulch! Your local garden centre should be able to help with compost.