PETG doesn’t stick to PLA and it’s often used as a support interface because of this. You could split the model up and glue the parts together after printing separately. But I don’t think it will help a lot with your issue. You may stop some heat transfer from whatever the part is sitting on outside but the PLA will still get soft and warp. You should just print the piece in PETG. Or try ABS. I find it prints excellent once you get the chamber to maintain 40-45°c for the duration and use an adhesive to stop larger parts from warping. ABS has lots of advantages, it’s cheap, and post processing is easy - easy to sand and paint, glue together with acetone, fill and smooth with ABS juice. And it’s UV and heat resistant.