First, a disclaimer: I am a Gong ambassador, thus I will take examples out of the Gong line I know a lot. But this is just to give you pictures and dimensions in real boards, so that you can find similar shapes at your favorite brand/shaper. I am am not trying to sell you Gong gear... which isn't available in the US anyways :-)
Dylan, at 63kg, for chop I would advise a volume of 63 + 10 + 30 = 103 liters. I.e., between 100 and 110 litres. 30 litres is your "buffer" (extra flotation) to dampen chop. For glassy conditions, you can get away with a "buffer" of 10, i.e. 83 liters. For your conditions, I would not go below 98 liters. Too much flotation (over 120 litres), and the board will feel corky, and will be less stable once you learn to balance when rails go underwater. Better add width and length for comfort than volume after the minimum is there.
For the width, it depends on your height. I would advise against going narrower than 30" for a 6' guy. Me, at 5'5" would not get under 29". I can balance on narrower boards, but they feel dead in windy waves and are too tiring. Narrow is for fast waves. Pros can use 25" (or less) boards, but they are paid for it :-)
Then, the shape: you want a fast rocker (flat) and width in the tail and nose to extract all the power of the wave. Not as round as a noserider nose, some kind of semi-pointed nose. Wombats, Eggs, Simsups, all these kind of "fun shapes" are good. I would be wary of round outlines that may be a bit limited in speed to maximize surfing time in your closeouts.
Finally, the length. If you already know how to shortboard prone, how to "pump" the board by small turns to gain speed, you will wants as short as possible to be able to throw the board around to create speed. Also, being patient enough to train to master the row on sub-7' on flat water is mandatory. But the shortest the board, the slower the paddle, and it can be hell against the wind. basically the ranges are:
sub-7': insane fun, especially if you like mastering new things. very slow paddling. Like the "ONE" (my favorite board for less than waist high waves) pointed by Kami in the 2nd post. A favorite for most people is:
www.gong-galaxy.com/magazine/pics/1-hour-4-boards/7'2' to 7'6": a good compromise. Still fun but paddles better. example:
www.gongsup.com/OD-7-2,1290.html?lang=fr Can be a do-it-all board.
7'6-8'0: "I don't want to spend time learning a new paddling technique: give me instant fun". More glide, less "pumbability". example:
www.gongsup.com/+PROTO-8-1-Fract-GONG+.html This is the board I ordered for my 60kg daugther, intermediate surfer (slow turns, does not pump), but not willing to suffer on a SUP.