I've fitted a Waeco kit to my car.

£59 for four heater pads.

http://cgi.ebay.co.uk/WAECO-HEATED-S...item5641d82d1e

These have two stage heating as well.

You could install just the pads and add the two stage switching if you wanted to. If you want to keep OE then wire in with both stages i.e. hottest. They are thermostatically controlled so it won't be an issue.