Is there a form file I could pre-fill for the "unable to travel" type of visa extension, please? I couldn't find it in the files page or via text search. Also, I wouldn't know what it's called or what it looks like.
TLDR : Answer Summary
The standard form for applying for an 'unable to travel' visa extension in Thailand is the TM7 application, which is used for all extension requests. In addition to this form, you may need an Embassy letter requesting an extension or a hospital certificate if the extension is due to medical reasons. Requirements can vary by local immigration office.