[Sirtel]

B&N Nooks are usually pretty good hardware, but their software is somewhat bare bones compared to others. Still, you can drag and drop your epubs to them (unless they've changed something about their later models) and you can keep wifi off or on without having to fear your books will be deleted.

Kobo Aura models are all quite old by now and batteries may be dead or dying. Still, if you don't want to mess with converting etc, and if you can get one cheaply, you could try them. Yes, you can just drag and drop your epubs to them.

There are also Pocketbooks. Also good for dragging and dropping epubs.

As for Kindles, all models newer than 10 years (and that includes all the Oasis models) use basically similar software and books can be deleted from all of them. The only "less aggravating" Kindles are ancient models and I certainly can't recommend them. Also, you'd still have to convert your epubs.