Unless your Ipad is a Mini it's a lot larger than the Oasis. And even the mini is quite a bit larger. So you might want to consider staying on the Ipad.
I'm the opposite. I like reading on a small screen so I've been reading on my phone for the last year or two. I do have some Paperwhites, both 3rd and 4th generation but my phone is always in my pocket so it's easy to pull it out and start reading. Also I prefer to scroll my text than to turn pages and I can do that with my phone.
Everyone says the screen is harder on our eyes and I've found that to be true unless I rest my eyes for a minute every half hour or so. As long as I do that my eyes are fine. And I can use that minute to think about what I'm reading so there's no loss.
That said, when the right phone with an e-ink screen comes along I'm going to be pretty tempted.
Barry