I bought a piece of 1.5 inch stiff foam to try to fix a sag in a bed. It didn't work but having that thick piece of solid foam around has been a life saver.
Need something flat to put a laptop on? Throw it on the foam. Going to be doing something that requires you to be on your knees for a while? Get the foam!
It went from stupid purchase to something I'd gladly replace if it broke.
What sizes are your monitors? Personally I think gas springs are the best, as any good one will allow you to adjust height and position with relative ease. Biggest thing you really have to watch for is the weight of your monitor vs the capacity of the stand, but if you're not dealing with huge monitors you likely won't run into this.