my 2 cents.....
1. external blinds are a must. plan them now so they can be built hidden in to the fabric of the house. we use ours to shade from the sun but also as curtains at night so don't have internal curtains for privacy.
2. just install AC
when i was researching i read a lot on here about fan coils and underfloor cooling etc and, in the end, it was just too complicated for me. not being able to heat water and cool the house at the same time just seemed a pain. so we planned for and installed ducted AC in the bedrooms and wall mounted units downstairs in a few rooms that we thought would need it. it is fabulous. the external blinds help and we have them automated to shade and follow the sun around but sometimes you just want to open them up fully and enjoy the view! so the AC takes care of the overheating and it's powered by the sun via our solar pv so i don't worry about running costs at all. our south facing bedroom has been a steady 21°C since April regardless of the outside weather.
keep it simple, install AC.