I have two booster seats in back, if we're talking about the kind that just use the regular shoulder/lap belts. One of my boosters is only a basic booster. The other is the seat base from one of the 3-in-1 convertible types. The basic booster seat works fine because it's a little narrower than the other one. The 3-in-1 base is wider and we have trouble getting at the buckle receptacle for that seat. The difficulty is partly due to the hip room provided and partly because it is recessed. Both of my boosters fit just fine with no troubles in my wife's CX-5. My older child is about to graduate out of needing the seat, so when that time comes, we'll retire the 3-in-1 seat and use the narrower seat for the younger kid.