The best camera is the one you have with you. Phone cameras have improved significantly, and you can get some great snapshots that way.
On the other hand, if you want to capture more artistic shots as opposed to snapshots, a "big girl camera" is the way to go. I just got back from 9 days on Kauai in Hawaii, and I'm SO glad I brought my pared-down travel camera kit.
If you're going to replace your camera, I'd suggest going mirrorless instead of a DSLR. That's the direction all the big manufacturers are heading - Nikon, Canon, and Sony - and if you get a 28-200mm lens, it's perfect for travel. You can go from a wide-angle landscape or sunset shot to a zoomed-in closeup on people or architectural details, all without changing the lens.
The best camera is the one you have with you; it comes down to what you're willing to carry. I used my phone for snapshots last week in Hawaii, but I got the best photographs with my Nikon Z7ii and I'm so glad I brought it with me. For a once-in-a-lifetime trip like you've described, I'd want the more powerful camera. But then again, I'm a photography nut.
