Can I switch from a Non-B visa to a Non-O spouse visa without leaving Thailand?

You should be able to change the reason for extension.

Better ask your husband to call immigration and ask for details.

If you’re now legally married to a Thai man, ask your local Immigration office whether they will let you switch your current stay from work to marriage, because practice can vary by office (sadly, a common inconsitency in Thailand).

If you are on a 1-year extension based on work, some offices may allow a change to a marriage-based extension at renewal, but if you are only on the original 90-day Non-B, you likely may be told to leave and apply for a new Non-O instead.

Do not cancel the work permit or job first until Immigration and the labour office confirm the sequence, because a Non-O based on marriage can support a work permit, but the switch has to be handled correctly.

Also, since you talked about being married but also mentioned a 400k THB deposit, may I assume that you are male, too (same sex marriage)? Because a foreign woman married to a Thai husband would not need to show any finanances. Short version: female foreigner + Thai man: usually no 400k listed; male foreigner + Thai woman: yes, 400k/40k listed; male foreigner + Thai man: legally should be spouse-eligible, but the public Immigration wording has not fully caught up, so that one should be confirmed with the local office before relying on either rule.

Why bother changing it over just stay on your work visa less hassle and you'll save our self a few baht...

When your extension of stay comes up for renewal you should be able to change the reason for the extension from working to marriage without first having to get a Non-O visa so no need to leave the country. Also as a female married to a Thai male there should be no financial requirements to meet.