Yes, you should Inc a letter of intent for the DTV plus as sole owner a letter giving yourself permission to work remotely in Thailand. Wise had been accepted for many approvals but for recently someone was denied an extension via a Wise account. Probably better to use a bricks n mortar bank account.
The DTV is for online work only, you need to demonstrate work that is done online while in Thailand. I submitted a portfolio which highlights the work/tasks to be done online.
An updated bank statement of 500K THB seasoned for a minimum of 30 days must be submitted when applying for a 6-month extension at an immigration office.
Regarding sponsorship you need to ask first who they approve as sponsors. Some embassies only approve of employers sponsoring. Location doc - utility bill, lease agreement etc. ChatGPT very useful for a sponsor letter.