Improve existing roof insulation from the inside
We had insulated the heated attic area with rock wool. After the winter, mold had formed on the wood. The reason was ice crystals between the wood and the rock wool. When thawing, the moisture has accumulated more and more on this layer. However, I don't have 2 cm PUR insulation on the outside. This certainly reduces the problem of condensation on the wood layer. It may not be easy to assess whether this will help 100%. 

In our case we had newly installed all insulation with an intermediate ventilation space (2 cm) between insulation and wood. There were no problems until now for over 10 years.