There isn't a simple answer as you need to start from where the
greatest risk is. *That isn't necessarily the wood burning stove if
half the family smoke! * Is the building one of more storeys? *Are
sleeping areas compartmentalised (have doors) Are you talking about a
domestic house or something else?

Thanks for the advice, much appreciated!

To go into more detail:

2 storeys, old chapel converted to domestic use.
All 4 bedrooms have doors, 2 upper floor, 2 lower floor - all open
into the open plan area (and have means of escape windows as well).

There's a modern oil-fired Rayburn in the kitchen (ground floor, with
doors) - which also has heat-sensitive cut-off valves for the oil

The upper floor smoke detector wiring is already behind plasterboard,
consists of single point outside the bedrooms, above one door - and
within 1.5m of the other door - also well exposed to the main space
with the woodburner.

The lower floor wiring could still easily be changed, and consists of
two points just inside and above the kitchen door (where I had planned
to fit a heat detector and a CO detector), - and one point under a
landing which is a natural catchpoint for smoke from the woodburner.

Another point the OP has drawn attention to - is placing them at a
height to make them accessible for cleaning - which is a particular
issue here.

Is it likely to be an effective solution (I would have to read up if
it meets regs) to have smoke detectors in each bedroom, and only a
heat detector in the main space with the woodburner?

I've just had a look at the cable routings, and changing to the above
plan wouldn't actually be too difficult.

Finally, what are the relative merits of rising-rate and fixed-point
heat detectors?