Agreeing with the above, the digital manga you choose will generally either have furigana or not in the files, usually depending on the intended audience age (i.e. shoujo or shounen manga aimed at elementary or middle school students will, and manga aimed at adults generally won’t except for unusual kanji or character names the first time they are introduced).
You can usually download a free sample or check out screenshots of the first couple pages on bookwalker.jp or amazon.co.jp or wherever you buy your ebooks from to see if it has enough furigana for you.
These threads are good to check out if you’re not sure where to start:
Resources for Starting to Read Japanese Content
Master List of Book Clubs
If your grammar is more advanced and/or you want to challenge yourself, there’s also usually thread on the forums of which books and manga are currently free on bookwalker:
The BookWalker Freebies Thread