First off, don't wear two pairs of socks. The friction between them will cause rubbing and blisters. You need a good quality pair of 2-season walking socks in the correct size (ones containing Primaloft or similar are good - expect to pay £12-15 for a quality pair).
Secondly, go and get your feet measured at an outdoor shop that has a good selection of sturdy walking boots. I'd say gore-tex or other similar breathable membrane is essential, as it lets the sweat moisture out but doesn't let moisture from wet grass/puddles in. Moisture of any kind will cause rubbing and blisters. Try your boots on with your walking socks, not normal everyday socks.
Lace your boots tightly enough to ensure good ankle support (you shouldn't be able to get a finger down the top of your boot) but not so tightly that it's uncomfortable.
Wear your boots in! Start by wearing them indoors for a couple of hours a day for a week or so, then when you know you're comfortable in them, build up your distance outdoors for a couple of weeks. No shop will accept a return once they've been worn outside so it's important to wear them indoors first.
Also hugely important to make sure your toenails are cut correctly (short as possible without touching the skin underneath, slightly rounded to avoid sharp edges). A toenail that is even slightly too long, or a touch sharp, will easily run a hole in the neighbouring toe when walking long distances.
I hope this is of some use. Enjoy your walk!