I vaped for 3 years before, and now that I'm back, I've still never used anything but drop-in coil tanks
Take a look at the original Nautilus. 22mm, holds 5ml. One of the most popular tanks of all time, an only recently discontinued. You'll be able to find them, along with their clones and parts, for years to come, and the coils aren't going anywhere soon, because they also fit a raft of other tanks by other manufacturers as well. The coil heads are inexpensive, and can be found in a variety of wire and configurations. I use the newer mesh ones.
The coil heads are great. Every tank that takes them that I've used gives nice, smooth hits, with very few malfunctions.
The Nautilus is a bottom filler, but it's also big, and very easy, actually, to fill and replace coils. The new Nautilus 2/2s (new, and helping to assure the continued supply of Aspire BVC coil heads) are both top fillers, and real winners, too. But they're only 2ml for the 2, and 2.6ml for the 2s. They're really easy to fill, though.