RX8Club.com - Hello all - from Loughton Essex

First post on here but rather than just a hello, I thought I'd make it count! ;)

I'm currently having some cooling issues with my 8 (2006 231) - the temperature gauge isn't actually showing an overheat (though I know how, shall we say, basic the stock gauge is) but I have seen steam from the expansion tank. I've replaced the fans, and I know they're working but they don't seem to be kicking in, my next thought was the thermostat. So, I ordered one online supposedly matched to my registration (I won't mention the site I ordered from) - went to fit it today, got the old one out and it turns out it's not the right part.

I'm not interested in buying a racing stat for now, I just want a standard one that'll fit but it seems that a lot of the sites that supposedly recommend certain parts for these cars haven't got a clue and will happily sell you parts that aren't right.

Does anyone have a correct part number, or even just dimensions of the thermostat so I don't get the wrong part again? At this point I don't care about brand, I just want something cheap that'll do the job for now and can be replaced sometime down the road. The RX8 is my daily drive and worrying about getting stuck in traffic every time I have to go somewhere is doing my head in!

Thanks!