Crydom has a variety of SSRs with built in circuitry control to handle a variety of input signals, i.e. from a thermocouple/RTD, 4-20mA, etc. I think some have ramp rate control and things like that.
Or, just get a proper PID controller with an internal relay or external relay of your choosing. Some PID controllers have jumper programming (or digital selection) of ‘relay type’. If you select SSR as your relay type, usually it will allow a faster minimum on/off period for better, more accurate control.
Unless you want to design the controller itself?