I recommend the Cosco 'Eddie Bauer' set that converts to the 80 lbs. booster seat. Last seat you will have to buy. I have it in blue (2 of them). Very nice. Easy in - easy out - easy to wash - watch out for the back feet and the marks they leave on the leather seat . I put a towel under the rear ones on my W124 wagon. I don't use a teather as this car ('94 wagon) handles car seats very well with the rear seat belt clips very exposed. They can really be cranked down unlike the W210 seats. Those are very difficult to get the proper tension. Always use 'H' clips too - less than 1 " from the seatbelt clip. Books for the kid in the car are recommend as well. How long is the potential time in the car with your daughter? What kind of W124? I am an expert in travelling with kids every day. Two girls (2 1/2 and 4 1/2 years old) to day care - 35 minutes one way. Good luck.