Hi Hugo, my recommendation is that you first try to understand what's causing those cracks.
In our boat, there were some cracks on the cockpit sole, that PO ignored, and were the symptoms of something major going on.
The tiller head was replaced, and poorly sealed, that leaked water through, and rot the cockpit floor core, and then everything else cracked, hahaha.
So I had to remove the rotten core, re-core (I did it with thickened epoxy), properly re-bed the tiller head, and then fixed the cracks.
I opened them with a dremel, and filled with thickened epoxy. sometimes I use marine tex, or the marine filler they sell at WM.
it can be just a crack on the gelcoat, or a deeper thing. Some people also use the cap tules for spider cracks, but I go with epoxy