There are smartphones, iOS devices, tablets. I don't know about the video recording via smartwatches but the ability to record video on mobile devices is remarkably easy to do and to muck up.
There are a lot of options; the trick is to find what works for you
and to be able to purchase locally or on-line. You might have an Apple
store near you but they may not have the exact third party product that
Same with Android folk; a tablet purchased at an office
supply store does not mean they will have a smartphone or
tablet accessories selection. This is my long winded way of saying you might need an online vendor. Stay safe; stick to the actual vendor or known online retailers.
Your greatest challenge and responsibility is to keep your device stable during recording. It isn't easy; the devices aren't necessary designed for ease of horizontal hand holding. Even when the content is compelling viewers shouldn't have to struggle to pay attention to what you have to say.
Tables owners; we share a special pain. Because as tough as it is to find a good smartphone stabilization product to record video it is a bit harder for the tablet crowd. But not impossible.
Square Jellyfish Tablet Tripod Mount might be what you are looking for; it is adaptable to tablets; doesn't block the camera lens and you can even rotate from landscape to portrait. I'm not sure that the tripod comes with the mount so double
check before purchase.
Please do not record unintentional vertical videos; especially on smartphones.
Joby makes an interesting line of products; for smartphone users you might be interested in the Joby GripTight Mount. You can use it as a stand alone device or attach it to other tripods.
Another option is Studioneat's Glif - this can also be used to attach to a tripod to help you keep it steady.
I hear some of you saying, "I don't want to carry a tripod." How about a monopod? The iStabilizer Monopod can be used to take Selfies or turn it the other way and record the rest of the world.
These are not so much recommendations as idea generators. There is a device that will help you take great video. You just have to find that affordable option that works for you.