My advice would be to get a deep cycle battery, but make sure the CCA
rating is sufficient to start your engine.

Because you will be running your entire boat off a single battery,
there is a greater probability that your battery may ( even
accidentally) become seriously discharged. The deep cycle battery will
stand up to the deep discharge/ recharge event better than a "starting"
battery.

Starting batteries use thinner plates to increase the amount of surface
contact with the electrolyte within a given volume of space. That can
produce more CCA. However, those relatively "thinner" plates self
destruct more quickly under the stress of extended recharge and chunks
begin falling into the bottom of the case where they can create a short
and "kill" the battery.

I'm a fan of a dedicated starting battery, but if you don't have
sufficient space and can only fit in a single battery, get the biggest
deep cycle that will fit. IMO