I love them but I wouldn't call the Harrington books "soft" by
any definition.
I also second the Elizabeth Moon and Anne McCaffrey suggestions -- McCaffrey's "Pern" series has so little science content that many folks will argue that it isn't SciFi at all.
I'd also suggest Orson Scott Card's
Ender's Game. The science in there is fairly understated, and it's certainly a very good story. The various sequels I wouldn't recommend without knowing how the first one was liked, though. Actually, I don't recommend the first set of sequels at all, but that's me.