Not ergonomic

Well, it seems like the 3d animation projects are going to take longer to generate any displayable results. It turns out the the table I thought would be perfect to use as a computer desk is almost right, just 4-6 inches to short for comfort. It's fine for watching movies or playing games, anything that allows me to lean back and slouch down, but I can only do a certain amount of detail work at a time before I get a crick in the back. Any suggestions what to look for and where as far as appropriate size and sturdiness objects to put under the legs? I mean four 4 inch cubes of wood would probably be just about right, but where would I get such things in a place that isn't timber country? I already checked the close by hardware store, and it didn't even have anything the could be improvised into what I need.