I am a Scot, and in N Germany for 10 years, but even that difference hurts in the summer 30C+ not unheard of, not much rain but reasonable humidity (winter is about the same). For me "too hot" is over 20 in sunshine if there is little wind.
My house is an old 1880s farmhouse with insanely thick clay walls and (most importantly) a half-metre-thick clay floor between the upper story (not renovated yet, just a music room up there). My house is 45 degrees to the compass, with my living / sleeping room facing SE, so shaded in the late afternoon, also theres a big bush thet grows tall and shady in the summer, and the apple orchard and (frankly overgrown) beech hedge shades the other big room (my housemates room) which faces pretty much South. The more W facing rooms (kitchen, small sitting room) are shaded by garden hedges and the smokehouse, and despite that the conservatory seems to serve as a bit of an evening heat trap, nowhere in the house seems to ever get above about 18C in the summer, or below 14C in the winter (with the heat on very low). The cooker has an exhaust fan that actually connects to the chimmney!
I do shut the living room curtains if I have cut the bush as then it gets over 20C.
Helpfully, it is almost always windy or very windy here.
I am an early riser, try to keep the doors and windows shut at all times unless it is cool (the house has enough natural draughts!!!) . I try to do my garden chores in the morning (where it is 12-20C depending) , but I react badly to mozzie bites so I have to mostly wear full loose coverup and a head net (not ideal, especially as I am light sensitive and old enough to need glasses for close work). Cutting the grass is the worst because though my mower can take the abuse of cutting wet grass, it is hard work!
I go most days to the river (10 mins walk) for a swim The road is at least partly shaded for most of the way.
I work from home on the computer, I have various locations for an outdoor desk, where the combo of shade (trees or a big sun shade parasol) and the almost-guaranteed wind mostly does the trick. Though, frankly, in the afternoon it is usually cooler indoors!
I am not sure how much is applicable to your more southern climate, but shading the building as you plan to is recommended, plus think about REALLY insulating your roof and upper storey from the sun.