Washburn rover -> Pickup

[Jsongs]

Hi
I have 2 Washburn rover guitars that I really like. These are small tiny travel guitars, but i seem to like these small guitars. The fretboard feels right to me and I like the .0010 strings.
I would like to fit in a pickup in one of them som that I can amplify it. Please help with a pickup recommendation?
Shall I go with a passive undersaddle pickup, or should I try a K&K mini?
Or anything else?
Thank alot for you help!