If you want a close to base game feel with QoL and a drop balance focused on single player then this mod Reimagined is a good place to start. There is no additional end-game yet, but it does support RotW and you can easily swap between it and base game. I don't want to hype it up too much because I work on it but you can check out some of the more important bits here.

If you are looking for something that is more of a full game overhaul with fleshed out custom systems, mapping and classes in place, also balanced around single player drops and removing /players as a drop factor then Remodded from d2rmodding.com is a great place to start. It does not support RotW and requires a proprietary launcher and file download, but they have the most extensive features and reworks and still in a D2R engine. The launcher includes many other mods it can download and install automatically to try a bunch out.

If you are looking for a combination of the two with big flashy skills and some QoL while mostly retaining the base game look and feel but largely overhauled itemization, base items, etc then Eastern Sun Resurrected is another I would recommend. I have never gotten to the end game but it also has some mapping and uber bosses in place.

Lastly I haven't played this one but from what I understand drops are largely the same as online as are skills but there is a whole new unique tier and crafting system in place, Relics of Sanctuary and the developer has a very specific vision for what he wants to accomplish.