Tescos is usually the one to go for, I used Sophisticat Pink on recommendation from a user on here takes a lot of cleaning but it works just the same.
I have capped mine with sand and in my heavily planted tank I used about 3" in the front sloped to about 5" at the back and a whole bag of playsand in my Rio 125. It falls through the cat litter but eventually it will start to sit on top, go careful when filling the tank and use a plate or similar ontop the sand or you'll disturb it too much and the cat litter ends up on the top again lol.
Have fun!