Jelster,
Apologies for being a little late, though this may help other people thinking of heading that way too.
I have worked in Botswana and Zambia running camps, and run group photographic trips, so hopefully can help a little.
I notice that your other half would like to visit a malaria free reserve, that would point towards Madikwe or Kruger/Sabi Sands in the dry season. Kruger becomes a malarial area when the rains start.
I also notice that camping is out, so that leave you with more expensive lodge options. I am going to ignore malaria in what I am about to write. East Africa will provide significantly cheaper lodging, as places like Botswana is significantly more expensive.
I mainly know Southern Africa, so will comment on that;
There are less expensive camps in Southern Africa, though they are more a one off and often in marginal areas where the game viewing is not neccessarily as good.
Botswana is very expensive if you are not willing to camp, particularly if you want to head that way in the peak season - you are looking at prices close to $1000 per person per night in most of the private areas. I love Botswana and it where I take groups, the whole northern part of the country is like one large game reserve, with no fences or people between national parks and private reserves. This enables you to experience a number of different habitats.
Namibia offers great landscapes, though game viewing is not a prolific, Zambia is good, though I did does no quite tick the box for me.
Zimbabwe is an incredible country to visit. Parks like Hwange and Mana Pools would provide you with an excellent safari experience. These areas can also be mixed with SA to give a real diverse experience. There are some excellent specials available in the country right now.
South Africa, good introduction, though it sometimes lacks that wild feel of the countries further north.
Even within each country, there are considerations like time of year -areas peak at different times. For example, whilst Botswana's dry season between Jun-October is supposed to offer the peak viewing, the large floods of the Okavango over the last two years restricts a lot the areas you can reach and in my experience, game veiwing can be poor.
The other aspect would be to consider what type of safari you are heading on. If your main interest is photography, you ideally need a private vehicle, or be part of a photographic group if you do not mind that. The private vehicles will be an additional cost.
In East Africa, there are camps like Serian, which inlcudes private vehicles in the cost of your trip - something to think about.
More than happy to help with more specifics where neccessary.......
I have a blog that maybe of some help
http://www.thesafariphotographer.com