Feeling the need to float around a plane of pure imagination? Try Astral Projection.
One of the main rules of D&D combat is to never let your arcane spellcasters get caught up in melee combat. Which makes it somewhat odd that Armor of Agathys isn’t just designed for exactly that situation, but entirely depends on it.
There are plenty of spells that require you to think creatively if you’re going to make the most of them, but only one of them makes you think with portals.