You already got good advice. I will add a few points.
I have both the DA18-135mm and DA18-270mm. Both are relatively small lenses (eg compared to the Sigma) and this is an advantage for travel. The DA18-135mm is the smallest, good overall and WR. It is the favorite of my wife who uses a K-01. Personally I prefer the DA18-270mm for its versatibility. I had a DA18-250mm before and the DA18-270mm replaced my old DA18-250mm which died of 'old age'.
KEH has recently a DA18-270mm for sale:
Pentax 18-270mm F/3.5-6.3 SMC DA ED SDM K Mount Autofocus Lens For APS-C Sensor DSLRS {62} at KEH Camera Store
and you might use the discount code:
KEH 12/18-EX and EX+ Sale-ends at midnight 12/18 - PentaxForums.com
I am a prime lens person (see my profile), but I value highly the flexibility of the DA18-270mm, enabling me to travel with one camera body, one lens, one spare battery, plus battery charger and flberless cloth in a tiny bag. Yet you cannot fault the DA18-135mm if it meets your needs.
My 5 cents.