I suggest you focus on the town of Ashland, right off I-5, which has a fun energy and is accessibility-forward. I apologize I can’t give you specifics on what exact places will have wheelchair accessibility, but I do know that the city in general makes effort to be so. Take a stroll through Lithia Park, which has paved paths that are mostly flat and smooth. There are a number of hiking trails in Southern Oregon, but I do believe they’d be challenging with a cane. Instead, I suggest the Bear Creek Trail section between Ashland and Talent (a walk/bike paved trail). (Note: while Medford is taking strides to make the Hawthorne Park area of the path safer, I do not recommend it for a solo traveler yet).
I hope this helps and have a fun and safe trip!