I just want to mention these gusy because they are a one shop stop for some: **broken link removed**
The SCR's do require a heatsink nd some thermal grease to mount and have various control inputs.
You should be aware that there are in general 3 modes of control for an AC line:
1) Slow cycle Triac/relay which is basically what you have (SST)
2) ZCP or Zero Crossing Pulse - This SCR control mode ensures that crossing occur at zero and thus uses a multiple of half cycles/ One half cycle is the minimum amount of power, other than zero.
3) PAP or Phase Angle Fired. In some cases you can get better heater lifetime, but line turn-on can occur anywhere. This allow a much finer control of power.
Furthermore, you can find a lot more varieties of AC line controllers. Some with current feedback, some with heater open detection, some with power measurement.
You might also consider a separate alarm module. I only had to do that twice in a system I put together. I really like Eurotherm, but their stuff is pricy.