Peat/sand/perlite might work, but there's also a good chance that it won't. Mexican pinguicula are generally easy to rot out in peat mixes. In any case, many, if not most inhabit alkaline soils in the wild.
Personally I think that chunky inorganic mixes are much better for pings, but everyone has their preferences. APS (Schultz Aquatic Plant Soil / Turface) seems to be the go-to soil, so that would be something to add to your shopping list.
Also, I keep mentioning rot, but it's not really an exact science. It's more the combination of factors that affect the growth of rot-causing pathogens (nematodes and fusarium/other fungi). Excess water and stagnation increase pathogen growth, while good watering practices, bright light, ventilation, and so on inhibit pathogen growth. Disease happens when one or more of these fall out of balance.