Having the bed shift on the wobbly springs mid print is very annoying so here is my answer. A cup part on one end and a post on the inside on the other. This tightly constrains the spring while still allowing plenty of adjustment range. These were made to fit my springs snugly. You might need to scale slightly.

Also throwing in my thumb nut extension part. They press on tight over the nuts that came with my printer.

Use the highest temperature plastic that you have.