Minecraft inventory space?

This probably sounds like a weird idea but trust me on this. Is there any possible way of changing the maximum amount of inventory spaces and maxing it less? Say about 9 spaces? I'm trying to create this pvp/spleef world for me and a few of my friends but in order to make it more fun i only want there to be a max of about 5-7 spaces available.

Well there are mods for that.

You can also take that mod, and edit it so you only get 9 inventory slots.