You have to go into the Malaysia so go though immigration and then see if they will let you leave the same day. People have been caught and charged with overstay in Thailand only leaving Thailand and not entering another country. Enjoy KL
the visa stamp has to be transferred to your new passport at the office where it was approved. UK assports have changed colour to black after they left the EU.
As you are married to an ex government employee , once the marriage is registered and you are issued with a pink Thai ID card you are covered by the universal health in government hospitals ( If I remember correctly its a max charge of 45b for treatment and medication) You wife will have to check with your local hospital to ensure your registered. I'm married to a former government teacher and have this coverage.
Maybe get you own plows and cases then wash them yourself to see if things improve. If the hotel does inhouse laundry go and see what powder they are using. Find a better quality one toh wash your self