86Regency

Hello, I have a 1985 Oldsmobile, and every time I go over a bump I feel the back side of my car rock from let to right and stuff like that. I am going to replace the struts, hoping this is why this is happening, but don't know which kind to get. I want to have a good "Cadillac-like" smooth ride, but that can handle weight, since I ride with my friends a lot in the back. I see on the auto parts heavy duty one, but seen that they are not smooth at all. I also seen some air assist suspension and I do not know what is that. I am guessing I have air suspension since I hear a compressor everytime I turn it on and off sometimes. Can someone let me know what kind to get. Thanks.