I make my own build surfaces out of 1.5mm thick G10 sheets. Since it is not attached to a spring plate, I had to come up with an alternative means to hold the plate down to the heatbed. These clips are slightly curved with a hook on the underside to grip the bottom of the heatbed and a lip on the top to apply downward pressure on the build surface. They are as unintrusive as I could possibly design them. These are set up to print in PLA, but PETG would be a better material to use. The fit is super tight, which is what you want in this scenario.