We have a 30kw log burning boiler (Bosky) which is on a vented gravity hot water & pumped radiator system. We also have an oil boiler in the return, just before the Bosky. A simple control system of pipe thermostats prevents the oil switching on if the water is already hot, but in extremely cold weather both boilers can work together for a fast warm up. We've never had overheated water - the oil boiler will just switch off once the required temperature has been reached.
95% of the time, we never use the oil boiler (too expensive) but it's useful to have as a back up. The only downside of the plumbing arrangement is that it's very inefficient to heat a hot water tank using just oil this way - the oil boiler has to bring the wood stove up to temperature first, so it acts as a radiator. However, the converse is true - most evenings we light a few logs in the Bosky which is enough to get a tank full of hot water for the next 24 hours, at virtually no cost.
I did assist a friend to plumb in a similar Bosky into a sealed gas system, using a heat exchanger, so I know that can be done too. On their system, a vented solid fuel system has a large water to water heat exchanger which transfers heat into the sealed system, thus reducing their gas consumption when the stove is lit.
We've been running almost totally on wood to heat 14 radiators for over 20 years now, with no problems apart from replacing the first Bosky when it reached about 25 years old (it was second hand when we bought it - the replacement was new).
Right now, we're busy splitting logs for next winter, using a tractor mounted splitter. About 12 tons a year is normal.
Find a sympathetic plumber or heating engineer - a combined system is not too difficult, if well planned.
John