Can I visit Thailand for 65 days with a visa exemption and get a 30-day extension?

Just so you know. There's no penalty in applying for your extension early, as the additional days, for this extension will be added to your existing stamp until date. Depending on your immigration office (determined by where you are staying) they will issue an extension with 30 or less days remaining on your stamp, others can be less accommodating and will only issue extensions closer to your stamp date. Check with your local IO once here, but there's no need to wait to the last day or so.

You can also make an appointment online for most offices, which helps speed the process. 1900THB is the fee.

I would contact your airline to make sure they’re going to allow you to board the plane. Some airlines will not allow you to board without proof of onward travel out of Thailand within the initial 45 days.

YES... You will be stamped in for 45 days on your Visa Exempt arrival into Thailand ...

Plus you can get One 30 day extension of stay at Thai immigration office for 1900 Thai baht.

So there is no need to change your planned trip to Thailand. Your dates are okay.