If relays is really what you want, probably continue down that path. I don't have anything fancy on our furnace either. It is a two-stage though. Didn't even realize that until we got the Ecobee because our original programable thermostat was only wired up with two wires When I put in the Ecobee I rewired with CAT 5e wire to the controller so I could fully control the furnace and the humidifier. Ecobee support was super helpful. I described the furnace control board the them and they told me exactly how to wire it. We don't have A/C, but the wiring is there now if we ever do add it (and after this Summer I think we just may).
Ecobee isn't like a Nest. Doesn't try to be smarter than you are. You set schedules and can fiddle with them as you wish. Temporary changes are just that. Schedule resumes and your temporary changes go back to normal. It uses Home and Away schedules if you want, and doesn't if you don't want that.
I like that it can save me some money by not just constantly running a fixed schedule when no one is home and then resumes automatically when we are. Really all I wanted in a thermostat, besides easy to use and remote access. Has all that, but doesn't try think for me. I've had mine for a couple of years. Never touch it other than to turn it off when my wife starts opening the house too soon in the spring and we pay to heat Toronto. Otherwise, I just let it do it's thing. I appreciate the nice extra features like maintenance and filter reminders which I set the schedule for. Then you have the extras like Alexa and Google Home integration and HomeKit if you want that.
Hubitat supported now, so it fits that bill if you're considering it.