Mine are from a local spring company. However, I have experience with TTC-1223v springs, which are stiffer than stock, and progressive, which means they get stiffer as weight is added, but still very nice ride. The same company makes a model called TTC-1211 that I think would be the cat's meow for most people wanting more carrying capacity, while retaining stock ride height, etc. Stiffer ride, but still nice.
Springs are actually pretty reasonably priced. I paid around $400 for the springs and install. One time deal. There are cheaper options too. There's a product called Sumo Springs that goes in place of the bump stops that would likely work pretty nicely. If I didn't go the route I did, they would have been my next choice. Last but not least are various air bag options. You can install bags that fit inside the current coils for under $100 plus the price of support hardware. Lots of fun options.
