Newer with less mileage for that budget?
Unfortunately I feel you will need to up your budget if you want newer and less mileage.
Finding an automatic F30 320d for R125k will be a bit of a challenge, for that price the mileage will likely be over 200k KM or it will be sold by a dodgy dealer and likely be a vehicle which was previously in an accident, repaired and is now for sale.
For that budget the E90 320d is a good option I feel. I would not recommend the 16i, 18i, 20i, 28i from the f30 range prior to the facelift when they switched over to the "B" engines. The N13 & N20 are not the most reliable engines and have multiple known issues.
With that budget in mind, an older BMW without any turbo charger (if you want to go petrol) otherwise a 20d from one of the E series is probably your best bet. It won't meet your year and mileage hopes though.
EDIT: A whopping 11 BMW's for sale on cars.co.za with under 125 000KM and priced upto R125k.