Depends on your passport nationality. If you also hold a Swiss passport, since you’ve stated that you live there, you can most likely obtain an income certification from the Swiss Embassy in Bangkok for your monthly income and apply based on that option.
Otherwise, if you plan to use income and a bank account outside of Thailand, you’ll need to apply through an embassy or consulate outside Thailand — unless you use a visa agent, which tends to be quite expensive these days.
Jomtien also also has a special rule that requires the 800,000 baht have been in your account for two months before you apply, if you choose to apply based on this option.
Generally there is no absolute answer to this, and you need to discuss it with your specific immigration office. However, several immigration offices do accept a joint account if, taken together, it qualifies in the same way as if you had applied individually.
You combine three months of pay slips or three months of pension payments into a single PDF file and upload it electronically in the e-visa portal as documentation.
The easiest solution is to apply for two 90-day Non-O visas based on retirement per year. That way you’re completely safe and don’t have to worry about an outbound ticket or spending time and money on an extension in Thailand.
Yes, not all agents can assist with this anymore and you also have to do it in connection with a larger package where you open an account, apply for Non O and an extension of stay.
You'll struggle without a Thai bank account. It's best to apply at home before leaving or in a nearby country if you don’t want to spend money for an agency.