*just been looking at another post relating to this.. I would also take a receipt for the hotel/accommodation where they are staying and the contact details/exact address.
I suggest you look through some of the recent posts here that relate to your question. Lots of reports from BKK and DMK of immigration officers scrutinising those with visa exempt histories.. proof of onward travel and 20k in Cash (not credit card or statement/document) - a must. Malaysian borders - also reports of some serious questions being asked and even refusals. Things have changed a bit since you were last here 😕
I think Bim Smith is confusing the TM30 document with the TM7 document needed when applying for a 30 day extension to a 30 day visa exempt.. if so it’s turned a very simple question into a complicated mess for the OP. 30 day extension to a 30 day visa exempt = a visit to Maenam immigration office, fill in a TM7, take a photo, your passport, TM6 departure stub, 1900 baht and wait for about an hour.
Tell your friend to fill in the TM7 and pay the 1900 baht. Can’t see how they’d suddenly introduce a hotel signature, lots of people tour the islands here and extend in Samui - it would cause chaos with all the backpackers if they did. Good luck 😉