gives the right advice! I have extended at Krabi - had the tm30 ready as I knew I might need it. They checked it online and saw it had been lodged & only wanted me to verify that’s where I stayed. You need to have the tm30 - even if for just the night before you go to immigration.
Many others have asked this question before & had to follow the same thing you ask here by staying / paying for local hotel (if their friend / landlord wasn’t able to get it done otherwise).
I’ve not used them. I’ve seen Mots in Pattaya recommended a lot when this question is asked. This popped up in my YouTube feed yesterday. They do everything- banks / licence / visa
You need a visa for Vietnam as an Australian - there are agencies that do “introduction letter” that enables you to get it “on arrival” but most are a couple of days. Probably some that can turn it around in a few hours - not sure.