@ga29, Sorry, I haven't used a walker for normal outdoors walking. I use one without wheels at night for my old man trips to the bathroom to prevent falls. For longer walks outside I've started using Nordic walking sticks. The link that I shared looked to be a good lightweight walker with a seat. Not sure you can find one much lighter than 13.5 lbs.
If it were me wanting to purchase one for myself, I would try to find a local medical supply store so that I could find something and try it before using it plus get advice from a trained therapist which most medical supply stores have.