Use high quality relays purchased from Digikey or another distributor (should be $10-30 in single quantities for AC mains) and put thermal fuses on the mains side of the relay (I generally put several, each going to different parts that are at risk of shorting). Slather everything but the heatsinks (add some if necessary) with fire retardant epoxy, carefully pushing the thermal fuse into the epoxy until it makes contact and pushes out most of the epoxy under the fuse.