First use the reception predictor here to find what sort of aerial should work for you and which way it should point.
Then use the terrain guide here to make sure you are able to mount the aerial high enough.
Then go somewhere like Trac (NB I’m not in any way affiliated and have only ordered from them once, but everything arrived the next day and when there was a problem with one of the products they instantly despatched another one to me - excellent service) and order the bits you need.
When you put it all together don’t use really cheap cable, make sure you use shielded, and if you can go for CT100 or WF100.