There are things you can add to gouache so that it does not smear. I like glair, which is made by beating an egg white until it is stiff, then let it sit until it separates. Pour the liquid that is in the bottom of the bowl into a small jar and discard the foam. The glair will keep for weeks in the fridge. I think some people add gum arabic. But my new solution to the whole gouache smearing problem is to buy the Acryla gouache. I LOVE it. It seems to have some acrylic in it, so it does not smear. For me, it has all the advantages of gouache and none of the disadvantages. I guess a disadvantage is that you cannot reconstitute it. But, I have lost interest in having lots of leftover gouache. I prefer to just use what I need and start fresh each day.
I know many people like Higgins Eternal, but I will say that in my years of teaching, the tip that most students found helpful was to try McCaffreys or Ziller ink and WALNUT ink. Those seemed to be the most beginner friendly inks. So, if you are a beginner, please don't limit yourself to just Higgins Eternal.
Having said that...I remember a workshop with Peter Thornton and we ended up using our dirty water to write. It was really soft an beautiful. So, if the only ink I had was Higgins Eternal, I would thin it down to gray and then it would not bother me.
And now for the ultimate in ink. Stick ink that you grind on a stone. It is the most heavenly ink ever. I don't know if anyone has discussed it on the forum, but it deserves its own topic. It is not rocket science to grind ink on a stone. And I have never seen anyone who did not enjoy using it. You do need to buy a stone, but it will last forever. The sticks of ink last a long time too.
Jean Wilson