painted floor

So I'm painting our awful floorboards with some chalk paint, and want to varnish over the top for a satin finish. Can I use any varnish (like Ronseal satin) over the top or does it absolutely have to be the floor varnish - which costs 4 times as much! The regular varnish has directions which say...

I have some sanded victorian pine flooring which I need to apply a finish to. I was going to paint it white, but now I am not so sure. Ideally, I would like to live with it for a while, before possibly painting it white. Are there any natural floor finishes that I could apply to it in the...