I have two set of stairs that mine use. One is a 3 step, it was a cheap one that I bought at Walgreens for $20 and it has held up great!! I use it for the couches.
The other one I bought is for my bed. I got it at Petco.
It has 5 stairs and is best for them getting up on beds or something taller.
And they all love the stairs and use them every day!! It is so nice because they can go down the stairs at night to get a drink or go potty without me worrying about them falling or hurting themselves. And it was very easy to teach them to use them. I am so glad I got the stairs and I think it was money well spent!!