Welcome to AAM Lucky 27.
Unfortunately your chances of success are small due to the €1000 in personal debt.
On a combined income of €70,000, your take home pay is about €4970.
The lenders will allow you to use 45% of this to fund your mortgage repayment so 45% x €4970 = c €2240.
From this figure the lenders will then subtract all personal debt so in your case €1000.
This will leave you with €1240 to cover your mortgage repayments.
This might not be far from what your repayments will actually be but the lenders do not make a decision on the affordability on today's rates. They must allow for several rate increases when they calculate affordability so they stress test at ECB + 2.5% (6.75%). Repayments on 300k at 6.75% would be about €1860 i.e a lot more than the €1240 you are left with to cover the mortgage repayments.
Your income is strong enough to support a €300k mortgage but you must try and bring your personal debt down to a much lower level.