Our 16-year-old cat was having a hard time getting up on the bed so we finally broke down and got these stairs, based on a bit of research.  They did not disappoint.  She loves them, and there's a side-benefit.  All her life she has hidden under the covers for hours whenever a stranger has entered the house.  Since we got these stairs, she is no longer afraid...go figure.

One tip...the mounting holes for the stair tops are not in the center.  Make sure to attach them so that they press up against next stair's supports.  It's sturdy that way.