My son is approaching the 18kg weight limit for rear facing in his Joie Stages and is nearly 4. It can be used forward facing with the seatbelt after this but it seems really heavy to me. In an accident, surely the weight of the seat would press him into the seatbelt quite a lot (as it's not fixed in as such) and risk more injury? Should I be looking at a more light weight HBB? I can't seem to find much advice online. Any advice is much appreciated.