When I first got Cali , she was 9 months old, I put her in a play pen next to the bed at night. I had stairs that went up the side of the bed, and did introduce her to those (she did not know how to go up and down stairs) . I would bring her up on the bed a little bit for playing, but then put her in the playpen.
She used a piddle pad in the bathroom faithfully. One nights out 4 days after I got her I went into the bathroom to brush my teeth. When I came out she was up on the bed sitting on one of the pillows and giving me "the look" - like, I'm sleeping here tonight. That was it
. We put the play pen away the next day.
She gets out of bed during the night and uses he piddle pad and then gets right back into bed. Sometimes I don't even hear her.
I think the issue is timing - she was ready and reliable and it works for us.