We serve a large number of clients across Thailand who rely on our postal services for visa extensions due to medical conditions or other challenges that make it difficult for them to extend on their own.
As long as theres a post office near them with signature delivery we can assist.
Your situation is tough, but it’s not unique to Thailand. If you were in the U.S. under a visa, you would face a very similar problem. U.S. immigration law also requires physical presence for most visa-related processes. If your visa were expiring and you were too sick to travel, you would need to apply for an extension (Form I-539), which requires supporting documentation, usually from a doctor (which you mentioned cannot be verified).
Our suggestion is to find someone you trust to send your documents to an agency. We offer nationwide services which sound like they would resolve your issue assuming you can find someone, and are able to let them in your accommodation to post your documents.