Solid State Relay replacement for SRD-12VDC-SL-C
You can consider SSRs (Solid-state relays). They're available in various ratings and qualities. You will need something of a heat sink at the 6A range. They can be driven directly with 3.3V or 5V logic and typically contain adequate isolation.
Photo from Digikey (note the safety approval markings):

Make sure your overtemperature system cuts off the actual power and not just the control signal- a frequent failure mode is stuck &quot;on&quot; permanently and ignoring the control signal.
Edit: There is no such thing as a pin-compatible SSR with those cheap relays, or most other kinds of relays, for that matter. Maybe some DIN-rail mount contactors have SSR doppelgängers that are more-or less compatible (probably with derated current capability).