It's a pretty subjective thing, but for me it's not a question of getting a tablet or an e-reader. Ideally, you want both. It's almost like asking "Should I get a coffeemaker or a microwave?". You can use the latter for making coffee, but it's so not the same experience.
I have had various iPads ever since they came out, and I love those devices. I use them for browsing, PDFs, mail, sometimes even watching a movie or a show, apps, and so on. I can even get work done on them! It's a fantastic little thing that I'd not want to miss. But reading novels on it never works for me. I get eye strain, the battery drains needlessly fast, there are distractions, it's unusable in broad daylight, there's glare.
For reading, I use an e-ink device. Those are much cheaper than a tablet and more simplistic, but being a specialized device they do the thing they are intended for superbly. Closest thing to actual books, and you only need to charge them every few weeks.
There are some e-ink readers that can run Android apps from the Play Store, but they always seem to use old Android versions and don't really come close to a proper tablet experience. Even your Fire 7" is more response and more capable in that regard.
So if your budget allows, I'd consider getting a tablet and an e-ink reader. A refurbished Kobo Glo HD will only cost around $99 or so. A decent tablet costs much more. I haven't found any modern Android tablets I am convinced of (and I looked), so I'd recommend a standard iPad, e.g. the 2018 model that just came out. Not very cheap, but it'll likely be supported and maintained much longer than any comparable Android tablet. If it does have to be Android, the Galaxy Tab seemed like the best choice when I looked into Android tablets.
If you have no problems with reading on a LCD display, a tablet does make a great multifunction device, but I do prefer coffee from a coffeemaker or a French press.