I used to get sucked into the "map trap" where I felt like I had to create these really elaborate battlemats and maps with high production values and over time I realized that 90% of my prep time was going into creating graphics and visual aids that added almost nothing of actual value to the game for most of the people running through the game, and it has the side effect of making people feel like they are on rails; that when they deviate from the carefully prepped scenario they're now in terra incognita or somehow transgressing. My advice is to use something like Roll20's mapping functionality, but instead of preloading maps, just turn on the grid and then use the drawing tools to quickly sketch out some rough features if people really need to know the tactical layout of a place, sort of like a virtual whiteboard. This has the advantage of being quick, still letting you maintain a tactical grid, and your players can still form an image in their mind's eye of a what a setting looks like without you overriding their own imagination.
Also if you really want to use visuals to help describe the look and feel of a place, create some folders on your computer and start saving images sorted by category and throw them on the virtual whiteboard or share them as needed via Discord or through something like Dropbox; I like to do that for exterior shots of buildings or otherworldly landscapes that are difficult to convey mood with just verbal descriptions.
As for systems that support gridless play? Basically anything that doesn't have super elaborate rules for facing, engagement, and combat movement, etc. should be fine: Old-school TSR D&D (and any of the one billion clones thereof), BRP, Shadow of the Demon Lord, Stars Without Number, Dungeon World, Savage Worlds, Call of Cthulhu, DCC RPG, etc. The more abstract, the better. Systems I'd avoid: D&D 3.x, Pathfinder, D&D 4. (I don't know anything about D&D 5th, but I've heard it can be played gridless, YMMV).