3 carseats...help!

I'm new to this site. We have a 2006 Prius. We are interested in trying to use it more as our "around town" family car, reserving our minivan for long road trips, etc. We have 3 kids ages 7, 5, and 3. The older two are big enough to be in high-back boosters. The youngest still needs a forward facing harnessed carseat.

Wondering if anyone has successfully and safely fit 3 such seats in the back of a Gen II Prius ('06). If so, what make/model of forward facing carseat and boosters did you use? We have Graco Turbobooster Safeseats, which are high-back boosters, we'd like to use and are considering buying a Radian 65 or 80 for the youngest.

I'm interested in knowing how hard it is to buckle the boosters in this arrangement and how tightly packed in the kids are. Can you suggest other boosters/forward facing carseats that would work better than the ones I've proposed?

I know it's not going to be spacious back there, but I don't want the kids packed in so tightly that they are jammed up next to the doors for safety reasons.

Any help would be appreciated!!!