My daughter's booster seat didn't fit great. It would work, but was wide enough that it pressed into the bolsters to sit level. Noticed one while looking at Wal-Mart that fits great. It's a Harmony Youth Booster model 0304003LRW. The bottom flares out like it was made to fit the Mustang's back seat. Also seems to give her a little more leg room because it slopes off in the front. Only $13.50.