Smart stat for grant boiler

Hi all, we’re finally getting to the end of our old house renovation..the plumber s fitted a grant vortex boiler..nothing fancy here, 1600 sq ft old farmhouse, rads, 3 channels,.. upstairs heat, downstairs heat, and hot water...
I’d like to fit a smart thermostat, and naturally, it’s far from straightforward...weather compensation, load compensation, opentherm...I,m kinda lost...we don’t need anything too fancy, ease of use is important, we,ve got an old fashioned timer in our existing house, and hate its clumsy features..hive and nest seem to be the heavy hitters, would appreciate some advice..