You need to do the math, SAC (Surface Air Consumption) and assume you will be breathing faster because of something that made you go to the pony in the first place times how deep are these wrecks you’ll be diving = what to buy.
I carry a 12cu ft and add a 19 cu ft deco bottle on deep dives but I can’t use that deco mix deeper than 60’ so the 12 needs to get me there.