Stackable switches

I have 2 3Com SuperStack II 3300 Switches which gives me a total of 48 ports. I have only a couple of ports left open on them. I would like to add more ports to my network. My switches have worked well and I am happy with them. Question how many switches can I stack? What switch should I stack onto my existing switches I really only need a 12 port switch max. Any recommendations would be greatly appreciated