I tried no map and also no portal at the same time. Yes remembering where you are especially sailing is hard. I ended up putting big arrow signs periodically on shores pointing the way back I came.

I found a yagluth ygvisir so I decide to take the opportunity and find the summoning alter. Even though I was still trying to find bonemass lol, and I'd already found modor at that point. So I ended up sailing across a really big ocean, I was freaking out I was never gonna find my way back. It felt like the island ended up being at the very edge of the map, probably wasn't. And then return sailing I ended finding a direction sign that was in a completely different area than I thought I was. I was just so happy I decided to put up those signs.

Anyway still trying to find bonemass I found an above ground ygvisir so it's just a matter of forcing myself in that one direction but there seems to be a lot of islands in the way that again might be throwing my direction of since I have to change course so many times