I also have a 2011 27" iMac which is a great computer but it's way past it's prime. I plan on replacing mine in a few months, this may be something you may also want to consider as our computers shortly will be 3 generations of Mac OS out of date and running pretty old apps. Not to mention the hardware is getting pretty old and could fail with no replacement parts available.
If you do intend to replace it, ensure all of your apps that you want to use or keep on the new computer are upgrading (or replaced) by 64bit apps as Catalina (the current version of Mac OS) will only support 64 bit apps. This means your old legacy apps must be upgraded if you want to continue using them!