Ask HN: Easiest way to build a mobile app that won't break upgrade path later?

I have a niche B2B Saas web app that is doing well and growing quickly.

We have finite development resources and big updates planned for the next few months already.

Our app is responsive and works well on the mobile web, but we regularly get requests for how to find our mobile app in the App Store & Play Store.

Eventually, we will build the best mobile apps we can, but in the meantime I would like to get thrown together.

I am curious how HNers would throw together a web app into the app stores when fast and cheap is the priority.

The only non-negotiable is that I have to own the app and be able to release our future work as an upgrade to this existing app.