have the first Discworld one on my Kindle now so will at least get through that one, I think. My sister tells me the first one isn't great but I should definitely read it for background information and then the others are much better.
I disagree with your sister - you really can jump in much later in the series and be fine. Common suggestions are Wyrd Sisters, Guards! Guards!, or Mort, which all give you starting points in the major sub-series (Witches, Watch, & Death respectively). And there are a bunch of stand alones as well.
Do you have any favorite sci-fi authors? - no blood and gore please, more future society plots.
Have you ever tried Jo Walton? Her _Just City_ is about a bunch of people trying to bring Plato's city to life. (NB: I haven't read book 2 yet) Ann Leckie's _Ancillary Justice_ won all the awards the other year and is about very different societies (in many ways it feels in dialogue with Le Guin's _Left Hand of Darkness_).
If you are open to secondary world fantasy/futuristic societies, Max Gladstone's books are really good (start with _Three Parts Dead_). _Goblin Emperor_ should win a bunch of the awards this year. _Golem & the Jinni_ is a historical fantasy about immigrants in NYC. _City of Stairs_ may have a bit too much gore, but it's a great worldbuilding. NK Jemisin's last two series have had great societies, not much gore. Francis Hardinge is shelved in YA, but her _Gullstruck Island_ is a beautiful work of prose with great societies.
For big society thinking, you might want to try Chine Mieville. I bounce off his works, but certainly he is very well thought of.