This was inspired by https://www.thingiverse.com/thing:2620000 which I made but found that I needed a shorter version. So I designed a couple of shorter versions taking many of my cues from that thing.
The photos with the support fitted to the bed are of the shorter one.
Later I decided that it would be better to mount the support above the carriage rather than below it because this would increase the clearance of the levelling knob above the frame. This required a hole for the spring to go into so that it wouldn't too compressed to allow levelling the bed.