Heat detectors vs smoke detectors

Our home has old dictograph heat detectors in every room, and every closet. I want to start replacing some of the heat detectors with smoke detectors, but the wiring in place is 2 wire looped from the panel then to every detector, then back to the panel. As I can not re wire every detector, is there anything I can do to help the situation? I can put in at least 4 smokes in the house on a seperate zone with new wiring, but would it be reasonable to also replace the old 135 degree heats with 135 degree rate of rise in addition to the smokes? Also, what brand 24v 4 wire smokes do you all use? They will be put on a monaco c-100 relay based (old) control panel. Thanks a lot.