I tend not to buy the UK deals on Disney tickets. There are reputable online retailers that sell 3-day 'Magic Your Way' tickets with a 4th day free. Decent value, and doesn't tie you into loads of Disney activities if you just want to do the main parks. In fact, this year, we've just bought 2 day park-hopper tickets as we're only in Orlando for 10 days and there's plenty of stuff we won't do this time around (I'm looking at you 'It's A Small World').
Also, you don't need to stay on site to use the free Disney transportation
Get to EPCOT (where most of the hotel shuttles will drop you off) and you can travel to any of the other parks for free.