DIY potting compost

I'm bumping this thread as I've been looking at vermiculite prices with a view to mixing up my own compost this spring. I've never done it before but I was so disappointed in the commercial compost last year, I thought I'd give it a try.  Any advice or comments welcome.

I only use vermiculite on the top of compost for seeds which need light to germinate, as it's good at holding moisture and stops the compost drying out at the surface. Vermiculite is probably too moisture retentive to be a large part of a potting mix and as it's so spongey it will collapse over time under the weight of the compost above. Perlite is my preference because it holds its shape (though you still can crush it between your fingers) and provides the potting mix with structure and aeration. Perlite is also cheaper than vermiculite.