there are a lot of brands to choose from, and all seem to have similar properties.
Some are easier to work with than others.
If you want continue using the gravel you have now, try this:
buy a small box of 1st layer pure laterite - you'll see it near the chemicals at the pet store, it is a small green and yellow box.
measure out the recommended weight for your tank according to the package, and then make small packets of it using butcher paper or wax paper and cotton string. Try to make the packets as small and tight as possible, to avoid the contents from mixing right away in your water. Take these packets and cram them all the way to the bottom of your gravel, spaced evenly across the whole bottom. Make sure you cannot see them from the top - they must be completely covered. After a few weeks, the bacteria in your tank will eat the string and paper, releasing the laterite into the bottom of your gravel. Now you can plant just about anything in your ordinary gravel and the roots will dig down into the laterite layer for their nutriants!
doing a gravel change to a "plant gravel" with water in the tank will lead to lots of dust problems and severely cloudy water. If you want to rebuild your tank or start another, you can just put a 3" layer of substrate down (lightly rinsed if you wish) and then slowly fill the tank with water.
some choices for you are: Flourite, Flourite Red, Schultz Aquatic Plant Soil, Seachem Onyx Sand, something called Eco-Complete Substrate and last but not least, plain old natural kitty litter covered with a fine gravel.