A ts can be used as a buffer so could lots of other things.
Your getting slightly boring ruining everythread with your fascination of stores.if you were impartial you'd appreciate there are certain places where a ts isn't the beat option but you don't you just constantly bang on about them.
Help the op and answer his questions without ruining every thread.
To actually answer the question,I've specified and installed numerous air to water only systems in properties your size to meet code 4 of the sustainable homes scheme which tend to mean no gas/LPG.
We've tried ecodan,altherma,some nebe units,and santo co2 Eco.
Of all of them the sanyo's performed the best,when paired with there acv cylinder theiyre a dream but not cheap.
If you've got PV,selling it back is the best option rather than self use,no point in going into that any further.
Biomas is the way forward,we do at least 1type of log,peat,pellet,batch,straw,coal a fortnight from domestic units to commercial plant.
Have fitted various with no problems,wouldn't look at stoves etc unless combining them with another source due to the heat output in the room they're in tending to be uncomfortable(for me anyway),these can be linked not just trough a thermal store but various other ways.
Pellet and gasification are brill if you have an outhouse etc to install them
In,very hands on.
Depending on availability of other sources their are things such as rape seed burners and waste oil,again hands on but awesome in cost saving.
Please don't even think about a danfos GSHP as that was the worst unit we've installed.