Homemade lactose free yogurt

Ok, my family is lactose intolerant. It's just milk though. We're fine with pretty much everything else, oh, except ice cream. I started buying Kefir instead of drinkable yogurts, because my son prefers to drink his yogurt. Kefir is 99% lactose free, which is a great bonus. Anyhow. The first round of lactose free yogurt was a little disappointing. I live in South Texas and I only have HEB done here. There are two different types of lactose free milk that are HEB brands. The first round of yogurt, I used the "Lactose Free Milk" HEB has. It's a lot sweeter than the other option and my son always thinks I'm giving him flavored milk with this one. Well, the yogurt was runny and elastic. There's a bunch of crap in the milk like guar gum. Guar gum in milk? I'm confused. So, I strained the yogurt for 24 hours and ended up making frozen yogurt out of it. It was really tasty and we couldn't get enough. So in anticipation of my parents coming to visit for my son's birthday yesterday, I wanted to make some homemade Greek yogurt to make tzatziki for the lamb they were bringing. This time I used the 2%"Mootopia" lactose free milk and used 2% Greek yogurt as my starter. (Last time I used both whole milk and yogurt.) It worked perfectly. I adjusted the recipe a little so I wouldn't have left over milk/yogurt mix. I didn't have quite enough to fill my 8 yogurt cups so I will adjust it again next time. I forgot to get fresh dill for the tzatziki, but other than that it was quite tasty.
Recipe:
3 Tbsp yogurt
5 cups of milk

The recipe says to heat the milk to a boil if it is not already treated at Ultra high temps to kill of any bacteria in the milk. I haven't done this step and haven't had any problems. If you do boil the milk make sure it is completely cold before you mix it with the yogurt. I adjusted the recipe to:
3 Tbsp yogurt
3 1/2 cups milk

Next time I will up the milk to 4 cups so I have enough to fill all my cups. Set the yogurt make to 9 hours and cook. Once it's done. Put the lids on the cups and cool in the fridge. And there you have it. I bought my yogurt maker at Goodwill. Totally scored. I've seen recipes for the crock pot but don't have one to try it in.