There are 2 financial requirements to extend a marriage visa - you need to fulfil one or the other.
Either : 400,000 in a Thai bank that you simply do not ever go below. Or 40,000 or more (not 1 baht less) EVERY month going into your Thai bank FROM ABROAD.
Your first port of call is the Thai embassy. I'm not sure what it's official name is, but there IS a visa often called "trailing visa" which can be used by relatives of foreigners. HOWEVER, Mr Covid has screwed up the normal course of things and several visa types are suspended for the duration of the pandemic.
Most countries require a covid test a set number of hours BEFORE DEPARTURE. A few places require it timed before ARRIVAL (Thailand isn't one of those).
This is really a matter for personal preference. Everyone wants different things. Our preferred hotel in BKK has always been the VIE. Others will be different.