I think £1600 if your net income is 5k is fine, I would find it easy to manage BUT my other costs are quite low (no other debt, we own our cars, not paying for expensive childcare full time etc). I also sit on a buffer of savings in case of job losses. I’ve had much higher mortgage repayment:net income ratios, but I knew my salary would improve over time so I wasn’t oppressed by the debt. For a few years, I was frozen in horror when I looked at the annual mortgage statement and saw how much debt we had. I hate debt.
Try and work out what is left after your necessary outgoings - eg mortgage, council tax, any other debt to repay, childcare costs, train season tickets, new pairs of glasses, school uniforms, insurance, car maintenance, Internet and Netflix (Essential in my home!) etc.
If it seems tight, then think about what you are happy to go without- holidays, meals out, new clothes, etc. And think about future earning potential plus the risk that one day you might face higher interest.
We have a cheaper house (and therefore cheaper mortgage) and we are overpaying as much as we can while interest is low, our aim is to be mortgage free by age 55. We don’t scrimp and save but we don’t live too extravagantly (other than OH’s expensive electric car). In our case. our house is lovely and I wouldn’t want to move somewhere bigger only to be all stressed about money. However if I lived somewhere horrid or tiny, I’d go without more of our little luxuries to live somewhere nicer.