Help searching for a used chair

Hello, I’m currently looking for a used manual chair. I’ve been using a folding 14” pediatric chair and made some adjustments to it but it is still incredibly hard to self propel. I’m in the process of going through doctors to get a custom chair but haven’t gotten anywhere as my doctor won’t write me a script without getting a full PT evaluation which takes months to get into. I found a chair on eBay for 500$ but it’s 12” wide but every other measurement is perfect to my body. Wondering if there is a way to adjust the chair to be wider. It is 12” wide but I would need at least 13”, the 14” chair is comfy but I definitely have lots of wiggle room on the sides which makes it even hard to push since the wheels have at least an inch probably more on each side. My current budget is under 650$ since I am unable to work. Curious if I would be able to add enough wheel spacing to make it comfortable. Boyfriend is a welder so he may be able to split the frame to add width as well. The chair I’m looking at is a tilite aero Z. Thanks for any advice.