ᐅ Basement in a Hillside House – Why Not Choose Insulation Materials Designed for the Future?

Hello,

we are renovating a house from the 1970s. The house features genuine sand-lime brick cladding (11 cm sand-lime brick – 2 cm air gap – 11 cm sand-lime brick), so we want to preserve the durable appearance and not install external insulation everywhere.
However, the basement is partially underground due to the house being built into a slope, and it needs repair/excavation because of leaks.
A specialist offered us extensive excavation work, 5 cm (2 inches) Styrofoam insulation, two-component bitumen thick coating, primer, etc.
The Styrofoam is intended only as protection for the waterproofing, but I am wondering if it would make sense for the future to install thicker Styrofoam or similar insulation now, since everything will already be excavated.
I estimate that in 85% of cases, we will not add external thermal insulation, but if we do decide to do so later (for whatever reason), wouldn’t it make more sense to use proper materials right away due to the excavation?
The additional material costs for 40 sqm (430 sq ft) should be in the triple-digit range.
What would likely be the appropriate insulation material for this?

PS: The sections of the basement in contact with the soil are reinforced concrete, not sand-lime brick.

Thanks in advance and best regards