On Corsican mint: I’ve kept Mentha requienii going 18 months around a tabletop fountain. Higher light helped, but the real fixes were cool nights (below 68°F), constant but metered moisture via a wick/SIP, and gentle airflow. In a standard pot it melted; in a 50% perlite / 30% coco / 20% compost mix with a wicking cord into a reservoir it stayed dense. Lime the coco lightly, trim monthly, and be ready for spider mites if RH dips.
Two underrated underplant options that haven’t been mentioned: Ophiopogon japonicus ‘Kyoto Dwarf’ for bright, cool rooms (slow, tidy, tolerates neglect), and Lemon Button fern (Nephrolepis ‘Duffii’) in medium light-behaves like a compact living mulch without the runaway stolons of creeping fig. Creeping Jenny (Lysimachia nummularia ‘Aurea’) can work indoors only if it’s cool and very bright; otherwise it stretches and attracts mites.
Functional gains are mostly microclimate, not room-scale: a dense mat raises RH a few percent immediately above the surface and reduces splash/evaporation, but you’ll pay in nutrients and competition. I have to feed the host plant more and do a thorough top-water/flush monthly to prevent salt creep under the mat. Also, mismatch kills combos: avoid pairing moisture-loving covers with succulents/caudex plants; they’ll keep the root zone too wet. If you insist on mixed moisture, keep the ground cover in a perforated insert and do a quick quarterly root prune around the insert with a butter knife.
One practical tweak for form: give the ground cover a low, side-mounted light to keep it compact; overhead-only tends to make it reach and thin out. And if gnats flare despite BTI, place a horizontal sticky card right at soil level under the foliage-catches emergers the fan blows past. Finally, skip hot decorative stones under grow lights; they bake stolons and turn nice mats patchy in a week.