three things to consider
I looked into this a lot in the last few years, and I have helped a couple people to do projects with concrete that look good finished.
A few points.
First, the law. Please note the legal difference between buying a thing that you carry into your house and buying a service that builds a thing that is structural in your house. Big difference. This explains why you will easily find people offering concrete countertops; it is simpler to sell, legally. And it is a thousand times simpler to offer to the general public on a web site, legally and commercially. By simple I mean that there is less risk of running afoul of the laws and regulations governing construction. Nobody likes being fined.
However the same concrete is used and the same skills are required, whether the application is a floor (made on site obviously) or a tub surround that you have made off-site and carry in to your house. If you are willing to hire professional advice, call a concrete fanatic who make countertops. If you are in Ontario or Quebec, call Jennifer McComb of Alchemystik. To come on-site and build something with you may require a licensed construction trade person. Exceptions exist under law too. You have to be able to understand how much and how many of the various risks you are assuming.
Second, the work. If you do the entire project yourself, that could produce great results too, but you're not going to be able to know in advance what it will look like, no matter how many people you pump for information so be prepared that you may have to backtrack, rip out and start over at some point in the process. You could just get to work without overstudying it, and learn while doing. Example: use a resurfacing mortar as a first layer to get the floor as you want it, minus a quarter inch, and then add a layer colored with a cement pigment. This top layer could be self-leveling cement or a high-performance cement like the product used for airport runways. You could put heating cables in your floor too. When you do the work yourself, you have a huge advantage over the hired professional, since you can decide how much daily progress is the right amount of progress; you don't have to make the project pay your bills for you, so you don't have to cut out the kind of steps that might lead to a few days wait here and there. There is no reason why in-floor heat cables will cause a waiting period, but it does take the time it takes and the average professional is sensitive to how much time the average buyer is willing to pay for, for visible progress. By the way, I know about heat cables, having done it for myself, for family and friends. I recommend you put heat in your floor.
Third, the look. What do you think of the look of epoxy finish on concrete floors? This is something you may have seen in commercial spaces, as retrofits or new. Do you know what smooth concrete eventually looks like on countertops? Do you want to walk on that same material / surface and risk dirtying it even more with shoe rubber, dirty feet, urine droplets and more? You can have that look, and seal it with almost "invisible" sealants.
David