How to keep an older house cool? Location: Africa

Hello and many thanks in advance for any answer!

We have been living for a few years in a bungalow from the 70s. Ok, it’s not located directly in Africa, but in northern Germany, although we also have warm summers here and the number of hot days is more likely to increase than decrease.

Now it sometimes gets up to 26-27 degrees warm in the house, at least on really hot summer days, and sleeping at night is quite difficult. The house is actually not in such a bad condition, roof and windows were renewed less than 10 years ago, so I find it hard to bring everything up to passive house standard here. Besides, the money isn’t really ‘planned’ for that.
During the day we already use everything we have to keep the sun out, roller shutters (not everywhere), blinds, etc.
At night, I only want to keep the windows open to a limited extent, since, due to the bungalow, all windows are also easily ‘reachable’ from the outside.
So I’m thinking about what makes the most sense and I’m a bit overwhelmed because there seem to be countless options. I understand that I will have to get advice at some point. But is there anyone who can objectively compare all solutions and not just promote their own?
That’s why I’m asking you, what are your opinions and experiences?
Climate split system (two indoor units)
Decentralized ventilation
Theoretically, a centralized ventilation system would also be conceivable to cover the majority
What do you think about ventilation with earth heat exchangers? Sounds pretty interesting.
Everything is available with/without heat recovery, with/without heat pump

Oh yes, if the whole thing is also more economical than our low-temperature oil heating system for heating in winter, that would of course also be interesting.

We have a fireplace, how is the risk of negative pressure there?

Living space is 165 sqm. The areas that would primarily need cooling are the bedroom and two children’s rooms. Maybe over the hallway and then it spreads into the rooms?

So, I find the subject complicated because of the many possible solutions. The most interesting to me seems to be decentralized ventilation, if it can also cool and be cheaper than oil heating. Also interesting because I can keep the windows closed and have significantly less risk of break-ins.

Really many thanks to everyone who read this long text and share your opinion with me. Hopefully, the text is written understandably.
Greetings from the north (Africa)

Roof fully equipped with photovoltaics (usually always worth it and shades the roof), consistently shade the windows, run the air conditioning during the day. The heat/cold distributes within the insulated envelope, so all rooms more or less benefit from active cooling.

The ventilation system does not provide significant cooling. This can be considered separately. Personally, I would probably retrofit good decentralized units in the bedrooms and living room.

Like all huts in Africa, install [Klima] and be happy...

Climate split system (two indoor units)

Cooling works

Decentralized ventilation
In theory, a central ventilation system would also be conceivable to cover most of it
What do you think about ventilation with earth heat exchangers? Sounds quite interesting.

Ventilation ventilates, but does not cool. For that, there are air conditioning systems.

Everything is available with/without heat recovery, with/without heat pump

Do you also want a new heating system?

Oh yes, if the whole thing is also more economical than our low-temperature oil heating for heating in winter, that would of course also be interesting.

If the heating system is not too old, replacing it will not pay off. What good is the expensive high-tech ground source heat pump if the heat disappears again through the building envelope?

Conclusion: Install an air conditioner and be happy. The units can usually also heat - after all, it is heat pump technology.

Roof fully covered with photovoltaics (usually always worth it and shades the roof)

Really good idea! I've thought about it too. But whether it's really worth it and I have some concerns that this might damage/make the roof leaky?

Ventilation system does not provide significant cooling. That can be considered separately. Personally, I would probably retrofit good decentralized units in the bedroom and living room.

So you would install decentralized ventilation in addition to photovoltaics and air conditioning? That could slightly exceed the budget

Ventilation ventilates, but does not cool. For that, there are air conditioning systems.

You also want a new heating system?

If the heating system is not too old, replacing it will not be economical. What’s the use of an expensive high-tech geothermal heat pump if the heat disappears again through the building envelope.

Conclusion: install an air conditioner and be happy. The devices can usually also heat – after all, it’s heat pump technology.

Well, I am somewhat looking for the all-in-one solution, as you might have noticed. A ventilation system could pump cooler air into the house at night. That would be better than nothing, but probably not enough on hot summer sweaty nights. Today I read about earth registers, does anyone know about that? A combination of ventilation with an earth register?

Our heating system is 15 years old; economically, it still doesn’t make sense to replace it, as you already said.

How economical is heating with heat pump technology of an air conditioner?