You are likely going to need a two person, sit on kayak if you plan to use it for diving as you will need space to store and secure your dive gear while enroute to your dive spot. Have you thought about what you are going to do with the kayak while you are diving? As a boat and kayak owner, I highly discourage people from diving from either vessel without having someone topside to deal with dislodged anchors, drifting, and boaters coming over to check out the seeming "abandoned" kayak. I know some folks drop anchor and hit the water, but more than a few people have surfaced to find their boat/kayak nowhere in sight because the anchor became dislodged, or someone decided to make off with their kayak while they were enjoying their dive. I also agree with Brad that you should rent one a time or two to get the feel of the kayak and to see if diving off the kayak is going to be your cup of tea. I found it was not as much fun as I thought it might be, far preferring to dive from my boat, but you may love it.