Yeah, defo do it yourself, it's easy. Me and the missus have had around 20 grand back between us up to now, and still waiting to hear from the last 2. With Barclays you can do it all online as well, and I'm pretty sure other banks/lenders have that option, though not all of them. The moneysavingexpert site has got tons of really useful info and documents.
Speaking of Barclays, they are by far the easiest bank to deal with regarding PPI claims. I had a claim on a Barclaycard rejected a few years ago, then last year out of the blue I got a letter off them saying they'd re-opened a load of claims, with a cheque for £8,800 attached to it. I claimed online with them last year for a loan I forgot I had back in the 90's, took about 6 weeks to get another cheque for just over 5 grand.
Best of luck claiming.