If you have neck problems then I would recommend the neck roll. If the bed is too hard for you, request a mattress pad from your cabin steward. If it's too soft then I don't know what to suggest.
The beach towels provided by the ships are basically LARGE bath towels. But I would suggest using them instead of packing your own. You can take the towels off the ship. You just need to return them when you return. You can take two if the size is not large enough.
It sure is fun being so close to your first cruise. Don't worry too much, you'll have a great time. I spent so much time figuring out what I needed to pack and I was so excited, that I forgot to pack the cruise documents, passport and airline tickets. Luckily I remembered about 1 mile from home.
Take Care and Have wonderful cruise;