I could also add something here. In 2016 I bought a sleeping bag from Hex Valley Down Products (http://www.hexvalleydown.com/). Their “standard” sleeping bag (plus a cheap FA dry bag) only weighs 1kg and is rated -10 extreme. They fill them with 100% pure goose down that is unrated but their guess is that it is 800+ fill power. The down is locally sourced and supports local economic development etc. Custom made according to your own specs (colour/shape/materials). I paid R3200 back then but it doesnt seem like their prices have gone up since.
It is for sure old school construction (the baffles are skimpy and the drawstrings need some smooth-talking to work), but for warmth + weight in the Western Cape it has only served me well. Ive only slept fully zipped in when the temps drop to 2-3 degrees or there is mad wind chill (caves/bivy style sleeping). I doubt you will find situations in the Western Cape where this baby will let you down.
Another plus point is the husband of the lady owning the company is Retief Jordaan, a certified mountain badass (just this year I think he won the Fish River Canyon Ultra 60+ division). Its nice to support honest locals instead of mass-produced bags that have been lying in their stuff sacks for months out the factory…
For another local option I could suggest Makoti down products, but I think they are in KZN or something. Damn this is starting to sound like a sales pitch but hey local is lekker!