Upgrading from really old DSLR Camera to a Mirrorless, but need advice?

So I guess I am what you would call an amateur photographer. I've had a Canon Rebel XTI DLSR for years now w/ the kit lense it came with. But I am thinking its about time for an upgrade to a newer camera.
I want to be able to be more advanced level than a regular point and shoot, but also can take video which could be used to create vlogs, and be small enough for travel. I want something to use for underwater photos so was considering looking into waterproof housing. Hoping to keep the budget under/around $800 lens included.

I came across the Sony A6000 and it looks promising. The negative reviews on the kit lenses are disheartening but it could be wonderful for me. The camera is decent priced that I feel like I could buy a Neewer/Meikon underwater housing (because I don't have the money for a Nauticam).it scares me about the possibility of it leaking and ruining my camera, though I have seen good reviews.

also interested in Nikon 1 AW1 due to the fact that the camera is already suitable for underwater, But I've read a number of reviews that claimed leakage and it ruining the camera, which makes me nervous.

I wonder if I'd be better off getting the A6000 or a cheaper mirrorless and buying a cheaper actioncam with underwater housing for any water photos on the side, like the Xiaomi Yi, though I feel like I'd be sacrificing quality of underwater photos. Even though I know the Gopro is good, it would probably put me over my desired budget if I got it alongside a Mirrorless.

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