We have one of these FP booster seats:
http://www.amazon.com/Fisher-Price-Healthy-Deluxe-Booster-Green/dp/B0000DEW8N/ref=sr_1_1?ie=UTF8&qid=1352777268&sr=8-1&keywords=fisher+price+booster+seat,
and one of these space saver high chairs: http://www.amazon.com/Fisher-Price-Space-Saver-Chair-Scatterbug/dp/B005IWM99K/ref=sr_1_2?s=baby-products&ie=UTF8&qid=1352777303&sr=1-2&keywords=space+saver+fisher+price+seat
My 2 currently switch off between them - using them both as booster seats now. When #3 needs the space saver chair, we will either move DS to the regular chair, or if he is still too short (which he probably will be), we will put him in another booster.