The DA 18-135mm f/3.5-5.6 WR is a good single-lens solution for travel photography when reach is paramount. I own it and like it. It is not the absolute best of which Pentax is capable, but it is a very competent lens, and if you live or travel anywhere where it rains a lot, a ubiquitous and affordable travel lens that you don't have to take off the camera on your travels can be worth the sacrifice in ultimate pin-sharp performance. It is sometimes included as part of a kit with Pentax DSLR bodies, and if so, is well worth getting as a package deal if you can afford it.
The DA 16-85 f/3.5-5.6, also WR, is from hearsay a good alternative when reaching out is not as important but wide field of view is (those two millimetres make a difference), and from everything I've heard may be a bit better optically (but is also more expensive). I considered it but rejected it because longer zoom was more important to me than wider zoom.
Pentax DSLRs are often found sold with an 18-50 or 18-55mm and 50-200mm two-lens set, which in its current form is weather-resistant. This two-lens set is an option I considered when looking for WR zoom lenses for my K-5, but then I figured that if I am actually taking pictures in light rain, swapping lenses is not something I want to be doing. Nevertheless, it would cover most of your needs in the early phase of getting used to DSLRs.
The kit lenses (DA L type) have a polycarbonate mount; there is an upscale version which has a metal mount. Opinions differ as to whether this matters. However, the DA L lenses lack quick-shift (the ability to make manual adjustments to focus without having to switch AF off on the camera body), which matters to some people when changing focus abruptly from near to far, or in low light where the camera might have trouble finding its focus point but can hold it OK when established.
Remember, too, that any lens you buy or have already bought for your K1000 will function on a Pentax DSLR.
The reverse is not always true - any lens AFTER the FA series will NOT work on a K1000 unless it's one of the earlier D-FA macro lenses (with an aperture ring, which the K1000 needs).