I've done this route (Madrid<->Málaga) on
Alsa but it was about 8 years ago now. There was a 20-minute stop at about the midway point at a kind of truck-stop/bus-stop/tourist-stop at a place with a bar, restaurant, and snack-shop as well as restrooms. I couldn't bring myself to try going to the restoom in the broom-closet-sized bathroom on the bus. The bus, as I recall, was quite modern, comfortable, and they offered up a movie on the monitors - if you understood Spanish.
July will be HOT but the bus will be quite nicely air conditioned. Still, the sun shining through the big windows can be somewhat uncomfortable if you can't reach the curtain to shade yourself.
Saludos, MadridMan
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