So, what's your floor plan like?
If you have an open floor plan, that lends itself to an RMH.
Heck, you could do radiant heating with an un-insulated tank in the center of an open floor plan, but without much control.
Are all of your walls insulated/ sealed or only the exterior walls?
Either way, unless there is an aesthetic objection, a lot of work could be avoided by running radiant heat pipe on the surface of the walls.
An old school radiator or a spiral of PEX pipe could offer a lot of comfort.
I like digging, but I find myself avoiding plans that require a lot of digging,, deep digging, or any digging involving roots, rocks and other obstacles, so real geothermal is out the question for me.
I like solar, but the space is an issue in my urban yard.
In a place with more space, I could see building huge solar collector.
As things stand, any collector would have to be mounted on the walls of my home, which is limited amount of square footage and already adsorbing solar, however poorly.
What is your land/yard like?
Maybe a rocket water boiler would serve you best.
A big un-pressurized, insulated vessel full of water heated by rocket stove exhaust.
Run a coil heat exchanger through this water to preheat your DHW, tap off that same exchanger to to feed your hydronic loop(s).
If you want to do solar thermal, add a coil for that.
Hydronic heating accepts all kinds of inputs.
One early retirement guru , Mr. Money Mustache, has a hydronic system that uses a conventional water heater.
If you have enough solar PV, electrical resistance water heater would work as a source for a hydronics system.
If I had a pond, stream or such, I would use it as a heat sink, with a coil heat exchanger being cooled in it.
That I would tie into the forced air system, experience suggesting to me that a even a room temperature breeze cools me off better than standing kinda near something very cold.