Socks, I do similar to you, use a cheapo cookie sheet above the stone. I think a 16" or 16.5" suits this kamado better than a 15", the one that came with it is 15" and as far as I can tell, is too small, lets too much heat past and chars the edges of what I'm cooking too much. My pizza pan is a rectangle and sits on the fire bowl but under the bi-level grill. Heat comes up directly from the two long sides of the cookie sheet. It's good enough for now and catches juices/fat keeping my kamado cleaner inside -- I like smoking large pork shoulders. At some point I'd like to improve my set-up but for now it works okay.
Thanks for the link to the ceramic grill store, Tallen234, I've bookmarked it to study later. I've cooked the most amazing grub on my Vision kamado, it's a huge pleasure to use after struggling so long on the old COS, you're in for a treat.
(Hey Socks, just noticed you're in TO, I lived there the first 42 years of my life!)