There is a list of visas on the embassy website. You could (depending on your nationality) apply for a tourist visa for up to six months. Take a look around then use a local visa agent jn-country). Or, save a lot of hassle and apply for a retirement visa before entry. (Then convert to a yearly extension to stay).
Sit down and negotiate, it's true (especially post covid) that people are skint. Invite her for a sit down and ask her to do a pre-inspection/indicate what (if any penalties) may be incurred. Be open about your concerns about the sofa and maybe you can come to an agreement rather than leave it to the last moment. Take a Thai friend or translator if her English isn't good enough.
There's absolutely no need to switch the reason for your extension - marriage to working. Perfectly ok to teach/hold a WP whilst on a marriage extension.