OP let me introduce you to my favorite series of all time: Konosuba: God’s Blessing on this Wonderful World. It’s an Isekai, or Japanese portal fantasy. It’s about four useless dickheads being useless dickheads on their way to defeat the demon lord in a fantasy world. They are lovable idiots turned up to 11. The humor literally split my sides open but it also has its heartwarming moments among friends. If you want a fun fantasy romp please give this a read.
Yen Press (and YenON):
Yen Press have many titles that fit your description of 'in another world' (isekai). I strongly recommend Konosuba (Kindle link)
And, for something closer to that of Ready Player One (in a game world), I recommend Overlord, Sword Art Online (becomes digitally available in May, starting with volume 1), and Sword Art Online: Progressive (way better than normal SAO, but no digital release, as of yet).
J-Novel Club is, pretty much, digitally exclusive. You can sign up to their subscription service, which gives to access to parts of LNs that are not yet available digitally in online stores, each week, but are removed from the subscription service once the volume is fully translated and in stores (such as after being published on Amazon).
Their site:
From them, I recommend to you Paying to Win in a VRMMO (title says it all), for something closer to Ready Player One. For isekai, Grimgar of Fantasy and Ash (already mentioned by someone else).. You may also enjoy The Faraway Paladin (reincarnation story), and <br> How a Realist Hero Rebuilt the Kingdom (isekai).
Sadly, arguably (well, imo) the best translation company, Vertical, Inc., doesn't have many digital titles available, due to being unable to get digital licences for series, most of the time. You can their titles, physically, such as Monogatari, from sites like Book Depository, which has free shipping world wide. I'll link their site:
Just so you know, I've embedded links to Kindle titles, sites, etc.
Isekai = Transported to another world. Do not call a VRMMO light novel an 'isekai light novel'. You'll be murdered.
And fyi: Kindle has the worst image compression. Thus, images will be of low quality. Light novels have coloured illustrations at the start, and black + white illustrations throughout the volume. You might wanna consider using Google Play Books, which will have J-Novel Club titles too, in about a month's time, or Kobo.
Edit: Don't use Book Walker, it's shit (my opinion).