My neighbor has the same problem, she has a 7 yr old that is 120 lbs. I wrote a comment on NBC13.com that the Texas lawmakers need to consider the "larger" children & ask what is a parent to do when their child's behind it too big to sit in a booster seat. I think for that age (7) they should put a weight restriction on it too, not just a height. Is a parent to be fined because their child will not fit in a booster seat? That was my question.
But to help you solve your problem, all I can suggest is take your son to Toys R Us, Walmart & Target & let him seat in the booster seats to "try them on" so to speak & see if you can find one that will work for him. I would say just the cheap 15-20 dollar seat without the back would be more comfortable for him. I had read they are only giving warning tickets until the first of the yeat, so maybe that will buy you some time too.
I did the same thing you did, I had just gotten my children out of the booster seat 6 months ago & here we go again!! Because mine will be 6 this year & will need one two more years I bought the turbo booster at Walmart, the back adjust up & down for their height & it is also removable. If you have another child that will be going into a booster seat after your son, I would recommend it. If not just get the one without the back if he can sit comfortably in one.
Here is the link to the Texas guidelines of safety seats.
Another mom posted it to a previous booster seat question.
Good luck in your search!
http://www.txdps.state.tx.us/director_staff/public_inform...