What type of visa should I apply for if I want to travel around Thailand for 3 to 6 months without making pre-booked accommodations?

Wait until next year, you may well find you can't travel around. Things are volatile here and change daily. There are areas like Burriram that you can't enter without a 14 day quarantine. In my opinion this place is heading for a complete lock down anytime from now.

You can apply for Single entry tourist visa(60days) at then extend your stay for 30days. If you want to stay longer you can change type of visa such as education visa.

Just get a tourist visa, plenty of options after that.

.F

Everything depends on when you like to come. Because now it’s difficult to go places. For the moment the tourist visa is extended till September…I know a guy who is here on T visa from January,and is still legal here till September.

Best advice is to hold off for a couple of months. I don't know if you're aware but much of Thailand is in a curferwed lockdown, with domestic travel severely limited. There are only a dozen or so domestic flights each week and none of them through Bangkok, so all travel is by road (limited rail) at the mercy of minivan drivers, or expensive taxi services. Anywhere you go, most things are closed. There is an almost nationwide ban on alcohol in restaurants, all bars, pubs, nightclubs are closed. Many beaches and all parks (national and municipal) are closed. Unless you have a desire to assist with rice-growing in Isaan, there's not much activity at the moment!

@Al**

get a single entry tourist visa from the thai consulate in your country before you wing your way here, come here, get stamped in for 60 days, apply for a 30 day extension AND during that 90 days LOOK for other long term visa options.

At this point you don't know if you wanna stay longer than 3 months and a single entry tourist visa will get you that much time

STV is being discontinued and was a crap visa for most.

Tourist visa is 60 days plus extendable by 30 days that gives you your three months required.