New Mac OS don't support older programs so be warned to upgrade to a newer version which is not compatible. If you tell us which version you have, we can tell you which OS would be compatible.
Thanks for your reply. I have InDesignCS version 3.0.1 but I also have other Adobe programmes and the same situation applies. Probably cheaper to purchase an older computer to run the software and upgrade what I have. Thanks again.
Your programs are quite old. I doubt that any newer version will support it properly. Yes, I think for your purpose it might be better to buy an older Mac.
InDesign CS vers. 3.01 (the first version of creative suite) is only Power PC code. It will only run on Intel Macs using Rosetta.
Snow Leopard OS X 10.6.8 is the last version of OSX to have Rosetta.
You cannot update your OS without your losing the ability to run your original CS programs.
Even going from 10.6.8 to 10.7 will kill your Power PC programs.
How old is your hardware? Which model?
It will probably make more sense to keep the programs on the current Mac and buy a newer one rather than buy an older Mac and trying to upgrade the current Mac.
Depending on what you have, there is only so much you can do to upgrade the hardware to keep pace with newer OS's and software.
Even if you can install something like OSX 10.11 El Capitan on your current hardware, there are newer features in the more recent OSs that simply won't work with the older hardware.