What visa options should I consider for multiple entries to Thailand during my trip?

This look rather a spam bot request quiz than a real question, but I will try to explain the difficulties you got Thai immigration offices are closed on weekends an public holidays and are open during office opening hours, so it looks very difficult to get a timing to get a reentry extension, also because ques will even your limited time frame shorter. So i think the reentry option is excluded due your time frame. Normaly the only problem is the que time (re entry is cheap) Also the option to first enter with exempt and than using a single entry visa is not possible because you do not got enough waiting time after the requesting of the visa and when you are getting the visa (takes a week a 3 weeks) so that is of the hookk also. So that rest you to apply for a Multiple Entry Tourist Visa (METV) but you need than the following standard documents and conditions:

• Valid Passport: Must have at least 6 to 12 months of remaining validity (depending on the specific embassy/consulate rules) and at least 2 empty visa pages.

• Application Form: Completed and signed via the official Thai e-Visa portal at thaievisa.go.th.

• Passport-Sized Photograph: Recent color photo (usually 3.5x4.5 cm or 2x2 inches, depending on the office) taken within the last 6 months against a white background.

• Proof of Legal Residence: Evidence that you legally reside in the country where you are submitting the application (e.g., residence permit, visa, or green card if you are a non-national).

• Bank Statements: Official bank statements covering the last 3 to 6 months showing a consistent, sufficient balance (typically a minimum of 200,000 THB—or roughly $5,000 to $7,000 USD / €6,000 equivalent, depending on your local embassy).

• Proof of Income / Employment:

• An employer letter stating your position, salary, and approval of leave, or

• Business registration/license documents if you are self-employed.

• Flight Itinerary: Confirmed/paid flight ticket for your first entry into Thailand.

• Accommodation Proof: Hotel reservation, lease agreement, or invitation letter with ID/house registration copies for your stay during the first entry.

• Fee: Around $200 USD (or equivalent local currency such as €150–€170), which is non-refundable.

• Validity: The visa is valid for 6 months from the date of issue (not from your arrival date).

• Length of Stay: You can stay for a maximum of 60 days per entry. You can leave and re-enter Thailand multiple times within the 6-month window to reset your stay.

• Processing Time: Usually takes at least 15 business days, so you should apply well in advance. The single entry visa is easier to get with less conditions but that is 30 days and you got to prolong that for another period in an immigration office , but got the risk your British starting carrier refuse you to board because your original 30 day VISA period is shorter than your+30 day stay Another piece of advice to not use the automatic gates because that change your status to visa exempt and your visa itself get worthless . A second option is to get in on visa exempt and come back in Thailand again on Visa exempt, You can extend than a Thailand visa-exempt stay by up to 30 additional days at a local Thai Immigration Office for a fee of 1,900 THB.

• Where to Apply: Go in person to the Thai Immigration Bureau office located in the province where you are currently staying.

• When to Apply: Submit your application before your current permitted stamp date expires. Do not wait until the final day.

• Cost: The standard fee is 1,900 THB (cash only).

Bring the following items to the immigration office:

• Form TM.7: Application for extension of temporary stay (filled out with a recent passport-sized photograph).

• Passport: Your original passport plus photocopies of the data page, your current entry stamp, and your departure card / Thailand Digital Arrival Card (TDAC) receipt.

• Proof of Address: A hotel/apartment receipt, lease agreement, or TM.30 notification slip showing where you are staying in Thailand.

• Overstay Acknowledgement Form: Signed form provided at the office. Option 3 is to use a third time a visa exempt after doing a visarun (leave Thailand before the 30 days are over and come back right away)

No chance you could move one of the trips, so you'll have no more than 30 days when you return?

You can certainly apply for single entry tourist visa that will give you 60 days. Then get your reentry permit on your way out to Cambodia.

You will not be in Cambodia or Vietnam long enough for a visa application. That means you'll either need to apply for the multiple entry tourist visa since your second trip into Thailand will be more than 30 days, or you'll need to purchase a throwaway ticket leaving Thailand within 30 days of your arrival so they'll let you check in to your flight, and then you'll need to apply for an extension in Thailand.