People will tell you that you need a co-founder because that's what everybody says; but I disagree.
It's not ALWAYS necessary to have a co-founder to launch a startup and there are plenty examples of single-founder startups that went big to prove it. If you can work on your own, just keep going like that until the product is live. Besides, you could also find a bad co-founder that'd drag everything down. Keep what works working and if you're able to build the product AND build a product that you think will sell then why fix what's not broken. Make sure to take time to read books and watch videos about entrepreneurship and business; I think you should spend at least an hour a day learning about what you don't know.
Most likely, it'll be very difficult for you to raise money at this point so if you can finish the product without raising capital then do so and skip the monkey game. Once your product is finished and starts to show even a limited amount of traction, then you'll be in a position to raise capital; in the meantime, you can prepare a business plan. As far as the business related steps that you need to take, you need to find a business lawyer to incorporate a business, you'll need an accountant and you'll need banking (make sure to choose a bank that offers online payments). You might also need a patent lawyer and see if there's a provisional patent worth filing for. You might also be able to get a loan from a bank to fund the very early launch phase.
Instead of a co-founder, I think you should go look for advisers. Everybody's going to want to give you advice, not all of it will be good. I think a good way to tell the value of an early stage adviser is to show the prototype one-on-one and watch the behavior. When faced with a business model or a product that's not yet validated by the market or by someone else, some people will glance at your product and, while you're explaining how it works, they'll just be looking for all the gotchas they can find to invalidate your product or your company: "ah ha, there's a bug here" or "ah ha, there's no co-founder". These advisers will not help you. Those who will help you will behave differently: they'll FIRST want to understand your product and your vision. Only hire and work with "infected" people who understand your vision. Take a look at this video of Xerox's CEO invalidating the computer mouse when it wasn't yet validated by the market.
You can build and launch a startup on your own. What you can't do is build and scale a business on your own. So good luck with your launch.