Buying a house despite having an apartment?

Good day, my wife and I would like to buy a house, but we have an apartment. We want to sell it, but actually only after we have bought the house.

Do we have a possibility or do we have to

move out into a rental apartment---> sell the apartment--> then buy the house

The house will cost 75 + 50 thousand renovation = 125 thousand
The apartment is worth about 110, outstanding loan still 90,000

In other words, even if we sell the apartment (high demand in Berlin) below value, we come out debt-free and will definitely get the 125 thousand (I am a civil servant, my wife is an employee with 2.8 gross)

Now I have often read something about mortgages, would that be an option for us?

Seemed that way to me - that should be quite doable, because it would simply be nonsense to move into a rental apartment in the meantime.