Over the years, I've read about spontaneous combustion in the news, but now I am wondering if it's possible.
Short answer: No, there is no evidence that this is possible. Reported cases can usually be explained by an external source of ignition (https://en.wikipedia.org/wiki/Spontaneous_human_combustion)
Edit: ok, let's add some more information..
The human body consists mainly of water and is therefore hard to burn. It nevertheless contains burnable material such as fat. Not to forget the easily ignitable hair and of course clothing.
If a body (or its surrounding textiles) is burning long enough, its body fat can liquefy and keep burning even on lower temperatures. This is called the candle effect. Like with a candle, the fire does not easily travel horizontally and can keep the surrounding furniture intact. In many cases, arms and legs remain mostly intact, which is probably due to temperature gradients in the limbs and a lower mass of burnable material.
It is though that in most cases the victims were already dead or unconscious due to e.g. drug intake before their body started burning. Often they were smokers or found in a room with an open fire place, which are possible sources of ignition.
Since victims often were alcoholic, one theory was brought forward that the flammable alcohol was causing an ignition within the body. But to bring the alcohol content of a body to a flammable amount, you would die of intoxication long before that..
This study posted by user1136 also mentions the points made above: https://www.jflmjournal.org/article/S1353-1131(00)90353-5/abstract
Yes, a body can burn. But there is no evidence that it can ignite spontaneously without an external source. There might be a few cases where no source was found, but that doesn't mean it wasn't there (a cigarette fallen onto the clothes would be burned). The media likes to push sensational news on "mystery cases", but that doesn't mean that humans just spontaneously turn into walking torches for no reason.