If you are using an MS120 then you are only using layer 2 switching. You can get a second MS120 and run it as an independent switch.
The MS210 supports stacking. So you could get a pair of them and stack them together. I frequently use these in office environments.
The MS250 support stacking and redundant power supplies. I typically use these as a starting option for data centres.
I guess it just depends on how much you are prepared to advance towards your goal.