We've used a few over the years, and this is my absolute favorite the whole way through - from 6 months - 4 years.
ETA: This can also make a great chair to use for the new baby when you travel (once the new babe is 6 months plus).
Both my two use the FP Spacesaver. I still have a Graco stand alone highchair which I will use until the older one is comfortable without the booster or get him a small booster cushion instead.
CD46 (6w 3d) 32DPO HCG 45,802 Progesterone 11
7w1d :hb: 140bpm
Make a pregnancy ticker
I have one like Laurie suggested and would definitely recommend it. DS2 uses it to sit at the table now. When he was younger I used it with the tray all over the house and like Laurie said would be great for travel...you can set it anywhere and feed them with the the tray.
Based on your ticker, your son is very close in age to my DD. We don't have a true highchair, we use this for our babies because it travels easily, doesn't take up much room, plus baby gets to eat with everyone else. Highly recommend this is someone is looking for a new "high chair".
ANYWAY, when DS was getting too big to eat in his Bumbo and was ready to move to that seat, I searched and searched for a booster seat to move DD too and ended up getting her this one. It's totally cheap but it's tall enough for my very small girl and straps securely to my dining chairs. Plus if it gets nasty, you can throw it in the dishwasher (not that it really does, it's all plastic). There are buckles if you want to buckle your child into the seat too but I took mine off because they were just in the way. I like that it doesn't have arms on it because she can get in and out all by herself.