Technology

You might try one of the larger Kobos to be able to read PDFs comfortably. The little ones might be a bit cramped with most PDFs. For html I've never tried that with Kobo, but a lot of people swear by the Android e-ink tablets from Onyx and Boox, though those are sometimes pricey!

I like my kobo

Also saying Kobo. I've got the Kobo Libra Colour and love it.

It's the only ereader I've ever owned but I used the spouse's Nook and Kindle a couple of times in the past and the Kobo kills it. Granted, we're talking about a nearly new release of the Kobo vs a 5+ year old Kindle so it's not a fair comparison.

Because of eInk and auto-sleep, the battery lasts me well over a month of casual reading (~30min before bed) with the occasional multi hour weekend session. Backlight is present and is totally readable in dark areas at <10% brightness; 100% brightness is like a supernova in your face. While the Libra Colour is not specifically a note-taking tablet like a reMarkable, it does just fine for quick notes/todo lists/etc but I did splurge on the ($60) stylus. There's a "notes" application that comes pre-installed.
eBook support for writing in margins (or over text), underline/circling, highlighting, etc is really nice but occasionally the highlight is flakey when trying to highlight the end of a paragraph. That seems to have been specific to certain epubs rather than an "always" thing, but it happens in around 20% of epubs I've used.

EDIT: Notes and highlights you do in an epub (and presumably other formats) are exportable to your PC via Calibre ("Annotations"). I love this because I like to highlight things I find interesting, particularly good quotes, and this gives me an easy way extract them while retaining a reference to which book it was and where exactly in the book it was. Example attached.

Seconding a Kobo. They have Overdrive (library) integration in the US and their eink and full color options are both great.

PocketBook if you want openness and long runtime (book-replacement), it runs plain Linux.

Kobo/Onyx if you want Android flexibility, with possibility to flash LineageOS/PostmarketOS (though they're slow for tablet use).

But personally, if you're not using it to transcript notes (recommendation Remarkable) or want more than merely reading books, i would go with a tablet.