The bacteria in yoghurt will also eventually break down the lactose into galactose and glucose, and consume the glucose.
I tried the GAPS diet back in early 2014, it did not work for me, but the long fermented yoghurt was good. I did the first fermentation in much the usual way: adding the culture (or a dried chilli) to sterile jars of milk that had been heated 85-90C for 30minutes or so and then cooled to 50C; and then keeping them warm in a yoghurt maker for 8 - 12 hrs. I just have the thermos type yoghurt maker.
I would then transfer the yoghurt to sterile la partfait jars and store them at room temperature as they continued to ferment until I needed them, maybe 5 days.
I did the same thing with kefir and coconut kefir (once I had strained the grains out.)
I have also tried, Tibicos, kefir, and coconut kefir which all seemed good for a time, and then became things I have an aversion too.
These days its just unpasteurised miso and korean bean paste, and home made lactofermented veges and kombucha. And a diet with lots of fibre
If I can manage to get the energy I want to try making the miso at home too.
GAPS pretty much shut me down, and coming off it I took a lot of commercial probiotics. The one I remember liking the best was O'Donnells flora balance which is Bacillus Laterosporus. I really don't like saccharomyces boulardii.