I tried a homemade salt water solution that I made with distilled water and rock salt and it set me back. I overused it and the little bit of normal skin that covers the top half of my top lip peeled off. I thought I was going to have this shit over all of my lips. Thankfully, that skin, which is more tender than it used to be, doesn't peel like the rest.
I, like you, felt that my lips looked better after two trips to the ocean and that's where I got the idea from.
I won't discourage you from trying it, but I would exercise caution.