You may also want to get a 1-2ft long one for travel.
I also use a tennis ball for my feet and a lacrosse ball for glutes and calves and some upperbody stuff. For other upperbody stuff that I’m not too comfortable putting lots of pressure between a hard PVC and my spine/ribs, I use a lacrosse ball standing against the wall and just lean into it for more pressure.
I had a 3" roller for about a year, and the other week I got my hands on a 4".
So much better :). I agree with the ~42" measurement, its nice to have room for both sides of your quads/hams/glutes, and your back as well.