Here is a link to an ebay tartan supplier "Myclantartan" with high ratings.

http://shop.ebay.com/myclantartan/m....id=p4340.l2562

He is also a member here on Xmarks. Most of the tartan he carries is lightweight and may give you the best of both worlds. His prices are quite reasonable, albeit for 11oz wool. He also has a number of not so common tartans. I recently purchased some Shetland tweed from him and had a very good experience.

Good luck!