After some research I went for "Joby UltraFit Hand Strap"
JOBY UltraFit Hand Strap with UltraPlate: Camera Strap + Baseplate
I also got the "UltraFit Sling Strap for Women" because I wanted the most lightweight combo and prefer the curved Strap
Camera Straps for Women: UltraFit Sling Strap for Women by JOBY . You can screw the Sling Strap onto the Hand Strap plate. So no need to carry along two (different) systems. It's also very quiet, no click click like on other systems.
This combination is very versatile, lightweight and still sturdy (I've used it with K-3 + FA* 2.8/300). The plate fits very well with the K-3. E.g. no need to remove it to open the battery door. I have not used it with the grip yet, so I'm not 100% sure if the Hand Strap is long enough for the K-3 w/grip. Though from the pictures shown on the Joby site, the Hand Strap should also fit cameras with attached grip.
Love it.