What are you worth?
I can't count how many times I had asked the question if I'm finally senior, or am I still junior. To answer that question, I formed assumptions, some of them correct, but many incorrect. This journey started 10 years ago. The technology "box" was much smaller and more defined then; everyone had been in the box for many years, so a comparison was relatively easy (or so I thought).
Basic principle #1: You're worth what someone is willing to pay you.
It's worth experimenting. Try it out on jobs you really don't care about. Tell them you want 50-100% more than you're getting paid now. Of course, never disclose how much you are currently making. See if you can start seeing patterns emerge for pay scales. Then target as near the top as possible. A lesson I learned a long time ago is, the more you get paid, the less painful the job is. It seems counter-intuitive, but believe it or not, companies that pay the top rates are simply looking for people to get things done, not micromanage.
Basic principle #2: Each company has their own definition of "senior".
So, you're the top developer in your company. That's great. Keep in mind that companies only hire talent within their pay scale, so if the pay scale is low, they get low-skilled talent. Once in a while, a developer will not know their worth and accept sub-par pay. It's worth finding out.
What if you step outside your company, how do you compare? You'll only know if you're truly senior if you try to get in to larger, more well-established companies. What if you can't hack it in one of those companies? Well, there's good money to be made being a top developer in a smaller company. And you can afford time to hone your skills before embarking on the interviewing journey again.
Basic principle #3: It's easier to be a big fish in a little pond when you don't live in a tech-hub city.
Tech-hub cities breed quality developers. At this point, a developer is a commodity, and pay scales will normalize. And these cities tend to be very expensive to live in because the salaries are generally higher and costs of living go up. From my experience, and conversations with others, you may be better off financially living outside one of those areas. And the talent pool is generally less qualified, so you can demand higher salary than most.