Can I check in a day early at Bangkok Airport and wait to board my flight to China without overstaying my Thai visa?

Hello, i am currently in Thailand and my passport is almost full (i still have some little space left on 2 or 3 pages, enough space for the small stamp of visa exempt entries but 0 blank pages left).

I plan to go to China and then go home from China. But my flight for China is on the same day as my last day allowed by my visa exemption in thailand, which means if i am not allowed to board in, i will have to take a flight the day after to go home, and therefore will get an overstay of 1 day.

I really want to avoid the overstay, i stay in thailand usually 6 months per year and i dont want to get more hassle in the future because of 1 day overstay.

Do you know if its possible in Bangkok to check in online and to through the immigration 1 day before the departure? And then to wait in the boarding area…?

Ps: 2 months ago i have been to China i already had 0 page left on my passport and it was ok at the immigration but the airline did not check… i dont need a visa for china and the stamp is very small, but now i really have not much space on my passport.

Thank you.