You are right that S. s. gigliolii (the southern ones) are more difficult. I have had adults for several years and only had a few larvae once in a while, whereas my S. s. gallaica reproduced every year.
Mine ate everything I fed hem (tenebrio, crickets, earthworms etc.). So that wasn't the problem. The aniamls did very well. I also could observe mating activities every year (autumn mostly). The female got thicker, but didn't produce larvae. I didn't provide them with running water, but just with a waterbowl (in which the gallaica reproduced without problems). I also kept my animals pretty dry, as a friend of mine had lost his animals keeping them too wet.
But....so I haven't got the solution for you, can only aggree that these are not very easy. But, that also is the case for several other Mediterranean subspecies/ species which tend to show calcium deficiencies if you don't take too much care on it (a problem the northern subspecies don't have show that clearly).
good luck, Sergé