Insulating basement and garage ceiling "thinly", with what?

I would like to inform myself in advance about what I could do to my house, (basement, garage) "could". I have an architect who advises me, but is currently on vacation, and I would like to gather theoretical information before the renovation starts. (renewing electrics, etc.)

The house was built in 1956, with an attached garage. Access to the basement is from the hallway (wooden door, or rather a normal room door) with a staircase. The entire staircase construction is made of wood, closed off towards the basement, and is very well preserved, it should also be preserved. The basement is about 2 meters high. The passage height to the individual rooms is about 1.90 m. I would like to insulate the basement ceiling as well as the wooden staircase construction (from below, i.e., from the basement side). All supply lines will be renewed, I will lay them along the walls and keep distance from the ceiling. However, the insulation should not be so thick that one always bumps their head, I am 1.89 m tall. What kind of material (or maybe someone can even name a manufacturer and type) can or should I use for insulation? The basement ceiling is not necessarily flat.

Also the problem with the garage. It can only be accessed from the outside. The garage roof used to serve as a balcony but was at some point converted 2/3 into an extension with a door to the remaining third which is still used as a balcony. The garage ceiling is only about 1.80 m high and there are double-T beams running along the ceiling under which the height is then only about 1.70 m. If I insulate only between the beams, would there be condensation on the steel beams? If it can be avoided, I would like to keep the height of 1.70 m as the car still fits in that way. In the garage, the temperature will be almost the same as outside since the gate is a very old wooden gate with a lot of air permeability.

Hello,

What kind of material (or maybe someone can even tell me a manufacturer and type) can or should I use for insulation? The basement ceiling is not exactly even.

Stone wool boards might be quite sensible here --> Isover
But: Individual measures are also subsidized by the KfW. They also specify minimum thicknesses.......

Same problem with the garage. It can only be accessed from the outside. The garage roof used to serve as a balcony but was at some point converted about 2/3 into an extension with a door to the remaining third which still serves as a balcony.

When was that done? It must have complied with some thermal insulation regulation then.

Regards

The total amount of the measure (50,000€) I have already completely allocated with my roof insulation and the new heating system, as well as the front door and a window, so I no longer need a regulation with minimum thickness for the basement. But I still want to do something and am not very familiar with the materials to be used, so I don’t really know what could be taken there. Your example was already a good start. The extension was also ages ago, there was nothing about thermal insulation regulations back then, it could have been around 1965-1970.