@sarahavian As you are not married, your son is currently the only one entitled to an inheritance. If you want your partner to receive something as well, you need to make a will. Keep in mind your son‘s minimal entitlement of 50% of what he would get by law, so half of your estate. You can therefore give your partner maximum 50% if you would like to.
Definitely look into the rules of your Pensionskasse. Also consider your pillar 3a. Without any other declarations, your son inherits it (you could also make your partner the beneficiary using a form provided by the bank). As far as I understand, your pilliar 3a is part of your regular assets (like any other bank accounts). So, also when deciding on the beneficiary for that, you may need to consider the Pflichtteil (there can be different beneficiaries for different 3a accounts, though, so this could also be worth considering if a lot of your assets is in those).
I would also consider a Vorsorgeauftrag. There is also the possibility to set up a document saying who should become your son‘s guardian in case something happened to both parents. I don‘t know the details on that, though, as I don‘t have kids.