I'm not actually that familiar with commercial ricotta since it's basically not available in Japan at all (and I've been here a *long* time, so I forget what it was like before I moved). However, I can give you my take on it. Whole milk ricotta is one of the easiest cheeses to make. However, there is a near infinite capacity to improve the quality. Obviously take what I say as a place to start, not a place to finish :-)
Souring the milk with a culture like you do is exactly the right thing to do. Apparently a pH of 6.0 - 6.1 is optimal for yield, but I suppose it depends on the milk to a certain degree. I don't ever measure the pH, so often I keep a bit of whey from drained yogurt to help if I guess wrong. Obviously a pH meter is going to be more consistent.
Usually, I raise the temp slowly to 85 C (185 F). The milk should start to break at that point. Then I raise the temperature fairly quickly to at least 92 C (198 F). This magic temperature is in pretty much every PDO standard for this type of cheese. My observation has been that at about 92C the milk starts frothing. I'll bring it up to that temperature (or a bit higher), waiting for the surface of the froth to start giggling. If it boils, you've gone too far, though, so you have to be careful.
As you raise the temperature from 85 to 92, you want to get a wooden paddle or something similar to scrape the bottom of the pot very, very slowly. Depending on the pH, the curd can stick to the bottom. This causes a couple of problems. First, it might form the curd at the bottom, since it's hotter there (if you are bottom fired -- probably not as big a problem if you are steam jacketed). We want the curds to float (for reasons I'll explain in a minute). Second, if curds form at the bottom and float to the top, they will kind of burst in a big bubble when it reaches the surface and disturb the floating curds (which we don't want).
Once you have a good thick layer of foam and curds floating on the top, kill the heat and cover the pot. Leave it for about 20 minutes. Whole milk ricotta has a lot of casein in it, which is what we make normal cheese from. However, it's surrounded by whey protein. Most of the foam in the pot is composed of that whey protein. The whey protein itself is albumin -- essentially very similar to egg whites. As the milk foams, you are cooking the albumin and setting it. The effect is basically like an egg white meringue.
With real whey ricotta, the cheese is almost entirely composed of that meringue (though you can add a certain percentage of milk to it... I can't remember how much, but I think 15% of the total). With whole milk ricotta, you actually have more casein than whey proteins and so when you do it well, it gives you a really solid, but light raft of cheese floating on the top. It's important to get that froth going, the casein to all rise to the top, and then let it sit undisturbed for the cheese to set for 20 minutes or so.
Once the cheese is set, you use a basket or a slotted spoon to scoop out the cheese and put it into a basket. I can't stress this enough: the texture at this point is really important. You *must* ladle it out and you *must* allow it to drain without being crushed. Edit: the cheese should *still* be floating on the top. If it sinks the bottom or hangs around in the middle of the whey, then the pH is too low and next time you should go with a slightly higher pH. You absolutely can't pour this out into a cheese cloth or you will end up with mush. Some commercial vendors call this "hand dipped ricotta" because you are taking the floating raft of cheese out by hand. The texture is completely different.
I think commercial vendors will put these in tubs to drain and it can sometimes be quite deep. I tend to limit mine to about 10 cm deep (about 4"), but I'm just making it for me. Let it cool down to room temperature draining in a basket, then chill it to 6 C (43 F) or so. When it's cold you can transfer to another container. I'm not sure if that workflow will work commercially, but definitely don't transfer it before it has cooled to room temp and has finished draining.
You can sprinkle about 1% of the weight in salt on one side, let it drain, then flip and sprinkle salt on the other side, let it drain and then put in a cool place. This makes a completely different kind of cheese, which is soft and spreadable, but you can slice it. Best if you age it in the fridge for at least 1 week, but you have to be careful of mold. It's hard to correct and since it's such a high pH cheese, probably not something you can do commercially, but... it is so, so, so good...
Anyway, I hope that gives you some ideas. I don't know if this will give you the texture your going for, but it certainly gives you a nice, thick, dense creamy cheese (while still being very light, thanks to the foam). If you do an aged version, the cheese slowly compacts over time and gets surprisingly dense -- to the point where you can easily slice pieces and pick it up with your fingers. It's got a nice spongy texture. But early on it's very light, while still holding it's shape.
