I can relate to some of your love-hate (maybe "hate" is too strong a word) of the ASK. I've been trying 2 basic approaches with my 12.9 Pro...
First, is to tote the Pro with the ASK attached. Although it is, IMO, the lightest and most convenient way to use a keyboard on-the-go, it still seems bulky (relatively speaking). When I'm at the office and want to use it as a tablet, rather than detach it, flip it over and reattach it (so that the microfiber side is against the back of the iPad), I'll just detach the iPad from the ASK.
The second, is to tote the Pro with only a smartcover. I keep a Logitech K380 BT keyboard on my desk in my office. When I want to use a keyboard, I'll use the K380. The K380 is nice because it can pair up with 3 separate devices (my 12.9 iPad Pro, iPad Mini 4, and iPhone SE). Great for those times when I leave my iPad home and need to Message with my wife, it's easy to use the K380 with the iPhone SE. When I take the 12.9 Pro to a meeting, I'll leave the K380 behind and use the onscreen keyboard and Pencil. If I know that the meeting will require me to use split-screen, then I'll bring the K380
Option #2 has been working pretty well so far.