This August, be aware that most safari places will be busy, it is peak season, so be prepared not to get your first (or second or third) choice. "before the first child comes along" suggests your girlfriend is pregnant (congratulations!). I am very risk adverse but I would seriously consider a safari destination that has virtually no malaria risk. The risk in August in Kruger or other eastern areas is very small, but the consequences don't bear thinking about. You could look at flying to Windhoek, hiring a car and visiting the wonders (desert, sand dunes, marine wildlife, flamingoes, coastline and safari) of Namibia? Etosha is very busy in August but you might find something that meets your needs and you can mix it up with other 'sights'. The coast around Walvis Bay will be around 20 C so pleasant.
Cape Town winter weather is not like the UK. It can rain or be windy and cool for a day at a time, but it will also have sunny periods, and when the winds are blowing from inland it can be dry and pleasantly warm (low 20s C). It is a great area to consider for whale watching (as per the advice above, if you do a boat trip look for a good weather window and go out early morning) and penguins, other wildlife including antelope, baboons and ostrich, winelands, picnics, and mountains and forests. August is prime time for whale watching, wildflowers and gardens (proteas) as well as the waterfalls. I admit it is not beach weather!
Or for a mixture of safari and beaches, the area north of Durban in KZN has a low malaria risk as far as St Lucia and Hluhluwe-Imfolozi game reserve. You could loop to see the Drakensburg, but I think 10 days could easily be filled with the wetlands, safari and then a few days at the beach north of Durban (temperatures in the low 20s C). There can be humpback whale watching at that time of year too. If 'some money' extends to £300-400 per night, then you can look at the private reserves that offer fully inclusive guided safaris in that area.
Enjoy wherever you decide to go, a fabulous part of the world!