we used yatch varnish. It is thicker so it takes less coats. It is a good idea to use a really cheap varnish for the first coat because the floor boards really soak up the varnish. This is the second house we have had that we have vanished the floors and I have to say it is worth the hard work. Make sure you clear away all the dust well as once varnished you can not get rid of it. Good luck
It would probably be more cost-effective to go for a good quality varnish that will last. I did my hallway with Sadolin, not cheap, but it's the stuff they use on shop floors so I knew it would withstand an enormous amount of wear. The only thing to watch is that there's a time limit between consecutive coats. I put down three coats and got a really professional finish that's going to outlast me!