If your not keen on the Luxi Crown, the Cargo Marathon is the next best 5 point that has wiggle room for both weight and height. It has 50cm shoulder straps, the highest slots available. My 3yo is 19.5kg and 115cm; still comfortably in the 5 point Cargo and will be for quite awhile. 5 points are tested with up to 22kg of weight so you have until that point before you need to move up to the adult belt/anchored booster combo.
If your needing a booster seat w/ adult seatbelt, the Infa Secure seats are probably the best on the market with a 4 star rating. We have a Vario Max.

Your other option is to import, but its technically illegal.