What is the best visa option for staying in Thailand for 86 days without issues?

Even a single entry (60 days) might not be enough. I know you can extend it and cover the whole trip, but the initial entry will be for 60 days, and all it takes is for the check-in staff to check their list of visa requirements, see it says 60 days, decide you're not boarding, and you have a nightmare scenario right there at the airport trying to explain how you will extend it once you get there with the check-in staff just looking at their screen which tells them your visa doesn't cover the length of your trip.......no trip. For the sake of £40 I'd buy a one way ticket Bangkok-Kuala Lumpur and show them that.

I agree with many of the posters on your thread.

Get a single entry tourist visa from a thai consulate before you wing your way here. Otherwise you might not even be allowed to board the plane to get here.

If your return flight out of Thailand is 86 days after you arrive, and you have no visa in your passport, you may have problems checking in to your flight. If your return flight is with them, they will see your return date and they will look for a visa that covers you for the entirety of your stay. If your return flight is not with them, and you essentially have a one-way ticket with them, they will also look for a visa in your passport, or proof of an outward flight 30 days or less after your arrival in Thailand.

The airline will have the responsibility (and cost) of flying you back home if immigration deny you entry at the Thai border, so they might not let you board the plane in the first place.

Best advice I can give you is to have a booked flight out of Thailand 29 days after you arrive (unless you are able to get some kind of Non-Imm visa which would allow a 90 day stay) and once you arrive in Thailand you can do all the extending of your 30 day visa exempt stamp that other people have advised you about.

You don't need to use the flight out, but you may need to show it to the check-in staff on your initial flight to Thailand.

Your stay is approx 86 days, many options:

Without knowing you're travel plans / circumstances here's 2 viable options.

Option 1 get a single entry tourist visa from Thai embassy / consulate in uk giving you 60 days and a 30 day extention inside Thailand (at immigration dept) for a total of 90 days.

Option 2 arrive on a visa exempt entry, giving you 30 days, again extend this by 30days at Thai immigration inside Thailand, then do an out/in 'border bounce' re-entering Thailand on another visa exempt entry for a total of 90 days.

At the border, without a Visa you only get a 30 day stamp.