Sorry, but I think they are far too similar. I know Ella is a traditional name on its own, but aren't they also both shortenings of Elizabeth? Aside from that Eliza is just Ella with an extra iz sound in the middle.
I have kids who's names are annograms. It is fucking nightmare. The second one took months to added to a goby database which impact health care, claims have been denied because staff can't see the difference. It's shitty. Still love the names but I might have chosen something else if I'd know it would be such a pain