If using monthly deposits,you won't need a bank letter,just a 12 months bank statement. And, you're correct,several immigration offices don't accept a print-out from a bank app.
I've been with Pacific Cross for many years. It's based in Bangkok and is a reliable insurance company with very good reviews. Loads of different plans and covers.
Just register and log in to the eVisa website and you'll be able to see the requirements.They do differ a bit compared to a single 60 days tourist visa,for example when it comes to financial proof. They also differ depending on nationality.