Congratulations on getting so close to publishing! That's always exciting.
Definitely use Amazon Kindle Publishing. Publishing your books through Kindle costs nothing, and has no effect on whether or not you also print hard copies of the book. I also use
Smashwords (Although, I highly suggest not looking around the site too much. Since anyone can publish anything nowadays, it's full of inappropriate books.) The good thing about Smashwords is, you can get into their premium catalog and your ebook will be distributed to Barnes & Noble for Nook, on iBooks, and other large ebook retailers.
Now, personally, I would stay away from any subsidy publishers. Typically, they charge far more than it actually costs to do your book, and chances are, the quality won't be worth it. Plus, you have to be really careful. There are so many scam companies. You have to always make sure you retain ALL rights to your work. Trust me, contracts are highly confusing.
I always recommend
CreateSpace. A couple of us have used it, and I've done all my books through it. It's owned by Amazon so your books are automatically listed for free. You can set everything up for free (Though I recommend purchasing their $40 pro plan since that cuts down the price of books and gives you more royalties. It pays for itself in the end.). The downside is, you have to do everything yourself. Cover design, interior design, etc. They do offer services like that, but those are pricey.
Hope that helps!