I realize that finding an ebook reader can be a bit daunting if you are only familiar with Kindle ebooks, so I checked out a variety of readers for epubs to see which ones work with my titles.
First and foremost, try the Kotobee reader. I use their software to create ebooks, and I have used their free reader for desktop and mobile use.
Freda is a nice little reader that works well with both text and fixed image layouts. It seems to default to white text on black (and reverses colors on black and white images), but I think you can change that in the settings.
Adobe Digital Editions is fine for desktop use for text-only epubs. It doesn't work well with images, though. You can't scroll to see all of an oversized image, so it's useless for fixed-layout epubs.
Mozilla has an EPUBReader file extension that works right in the Firefox browser. It seems to work OK. Can't say the say about the various Google Chrome extensions for epub readers, though.
IceCream - worked fine for images, but doesn't keep all text formatting. (Blank lines disappeared.)
Sumatra PDF reader: worked fine with epub if you just want text, but doesn't show images at all.
If you're buying ebooks, make sure you are placing them on a cloud server: I use Dropbox, but OneDrive, Google Drive, and others are also useful. I can get to the ebooks on my PC and also my iPhone through the Dropbox app, and the Kotobee ebook reader app on the iPhone will open up directly from Dropbox.