Elizabeth, hope you have a fantastic time in Thailand. I've always enjoyed my trips. A few tips I didn't see. These are conservative tips. Around the tourist areas it's not a big deal but when you get away from them Thais are pretty conservative. Only a few of these might lead to anything being said but following these will help you get along.
Don't wear shorts. Pants or Capri's are okay but they really expect women over 40 to wear skirts or dresses.
If you are going to any religious places wear either a full length dress or skirt. If you don't they will ask you to wear a wrap they will provide, and they are hot. This is also true at the royal palace.
Don't wear sleeveless tops. Short sleeves are okay but bare shoulders frowned upon. Not too much cleavage.
Never wear shoes around a statue of Buddha at a shrine, even if it's not at a temple. Many places have a small room or sectioned off area with a shrine to Buddha. This is one of the only ways to anger Thai people. That and insulting the King.
Don't touch anyone's head. Don't pat a child on the head either.
Don't whistle.
They consider feet dirty. Don't point at or touch anyone with your feet. This is insulting.
Do not step on money. Thai baht has the King on it and feet are dirty. This could get you assaulted. Would almost certainly get you cussed out. I was on the tram platform once and my cousin dropped a few loose bills. I stepped on one to keep it from blowing away in the wind. Only time I've ever felt threatened in Thailand. Had about 30 people glaring and muttering curses at me. I got on a different train.
If you ride a scooter taxi, keep your knees tucked in. They like to cut it close on the turns and if they ram your knee into a passing truck they will leave you in the road with a broken leg.
Tuk Tuks are fun but a taxi isn't any more expensive usually. Sometimes taxis are cheaper.
Always try to negotiate prices. Just about everything outside a proper store is negotiable. You'll spend a lot of extra money if you just pay asking price for everything.
Every taxi or tuk tuk you get into will want to take you to a jewelry store or clothing shop. Sometimes both.
I agree with Korean Air. Their economy seating is about as good as premium economy with anyone else. 34 inches between seats, pretty good food, they give you slippers to wear on the flight and headphones and a toothbrush. Usually a pretty good selection of movies to watch as well.
Don't be afraid to go to the hospital if you get sick. I had a severe upper respiratory infection my last trip (brushed my teeth with the tap water one morning) and went to the hospital. Went in, saw the Doc. Was referred to a specialist that did a swab of my throat and sent it to the lab. Got an antibiotics shot and 5 prescriptions filled at the hospital. Was there about 4 or 5 hours and the grand total of my visit was right at 62 dollars.
Take a photo copy of your passport and have it laminated before you leave. Carry that around instead of your passport. Just a copy wont do but if you laminate it then you're good. It gets damn hot over there and if you get your passport wet and it curls up they may not let you get on the plane to leave.
If you have the money to spend go to the tiger temple. Last time I checked it was 5000 baht (140ish US) and the ride out and back from Bangkok is another 50 to 100. It's an all day thing but bottle feeding tiger cubs in the morning and playing with the grown tigers in the afternoon, there's nothing like it.
I'd hit Nana Plaza over Soi Cowboy, but both are okay. If you go to Nana then go in Angelwitch. They put on pretty cool little shows every half hour or so. Spanky's is cool too but they have these plastic tubes they hit each other and visitors with. They are loud but don't hurt.
If you go to the beach don't rent a boat or jetski, they are scams. Don't go parasailing behind a boat. Most of them don't really know what they are doing.
Alright that's enough rambling from me. I promise all this advice is worth at least what ya paid for it :P