Which material should I use to print a mounting adapter for the y-carriage? I have purchased a replacement bed for my 3D printer. I wish to have it mounted on a single linear rail.
Currently I am unable to drill properly into aluminum (due to problems with my drill).
Therefore, I'd like to print and use an adapter piece/plate to fasten the Y-carriage to the linear rail block. The bed has a thermal insulation foam so the area around the bottom of the Y-carriage plate/bed assembly doesn't seem to go over 60 °C.
My question is:

Which material should I use for this adapter piece, and why? (I have access to PLA, PETG and ABS.)
Should I use threaded inserts or fasten the Y-carriage with nuts?

Please see the image below to have an idea as to what I mean by an adapter.
Any thermoplastic is a bad choice to carry a heated bed. For an unheated bed, monolithic (cast, not printed) acrylic plate of sufficient thickness can be used.
To get the needed stiffness and temperature resistance, steel plate of about 2+mm is the best choice, followed by aluminium of a higher thickness. The latter can be sawed with woodworking equipment, if done slowly.