Some type of silk or polypro as a base layer. Some folks wear a rash guard, they come in short and long sleve. They also make rashguards that are like thicker. Micro fleece is a good 2nd layer. If it is just a splash jacket, your going to get wet, rolling or not. You may want to look into some wetsuits alos. Most paddle shops will have all of this gear. NRS has some good layering stuff to check out. It's hard to find a happy medium. It can be 75 out but the water is 48. I have heard rule of thumb is dress on the warmer side (you may be in the water extracting a boat for 20 mins), you can always roll to cool down. Most guys at the local shops will point you in the right direction.