The minimum recommendation to move kids into a booster is 4 years & (not or) 40 pounds -- according to the National Highway Traffic Safety Administration + American Academy of Pediatrics (unfortunately, many Peds are not aware of their own AAP policy statement)....
There are often various ways to rearrange finances to afford a safer seat, maybe we can help with some ideas? I personally have gone so far as selling an item of furniture for the sake of my child's safety
The lower priced extended harnessing seats include the Sunshine Kids Radian & Cosco Apex. Higher priced options include the Britax Regent & Recaro Young Sport.
- Radian is difficult to install (have a technician help you)
- Apex is flimsy & therefore requires tall vehicle seatbacks or adjustable vehicle head rests
- Regent has the highest weight & height limits
- Recaro only has 40# weight limit but taller harness slots than your current seat & becomes one of the safest boosters available
Although the Recaro is expensive, you may save $ in the long run if you compare the option of buying one of the other seats for harness + a dedicated booster eventually. The Apex also becomes a booster, but it does not offer the excellent level of side impact protection as Recaro.
The "best" seat fits the child, fits the vehicle & is always used correctly!
What is your vehicle year/make/model