Usually my first approach to failures like this is threaded inserts (example), but since you mentioned it being MDF I'd go with connector/cap/dowel/etc. nuts (example). In either case I pair them with furniture bolts (example) slightly shorter than the combined thickness of the wood pieces.

The flat, flared heads on the nut and screw provide clamping over a larger area than adding washers to standard fasteners, making a more stable joint even through damaged wood. The low, rounded head profiles also greatly reduce the possibility of their catching on anything such as bedding or body parts.

Here in the US I'd usually find them at most local hardware stores, or always at one of the big box stores. For thicker joints I've used a pair of nuts coupling a section of threaded rod.

I've a nice, old desk chair that unfortunately the wood frame has degraded that's been held together quite solidly for years with this type of repair.