Unless you have the cash flow and modelling skills to plan out the next 20 years, see an advisor who can show it to you in graphs etc.
You need to budget for all your costs up until the youngest leaves uni, work out how much you can save and how much you could budget to downsize by to release capital / reduce mortgage at that point.
Budget for life insurance and critical illness insurance, relying on paying a mortgage in your 60s becomes more of a risk.
A lot can happen to earnings over 20 years in the face of AI, the economy, your health… and hardly anyone wants to work f/t to 70.
The years between stopping working and state pension kicking in need saving for.
Your best saving years (in whatever way is best: pension / overpayment etc) are the next 5: no or low childcare costs, none at Uni.
Start by doing a realistic actual budget if your outgoings, weekly , monthly, annual costs.
Add extra costs that you may not currently pay: buildings insurance, building maintenance, fund for new boiler.
Your starting pony is your outgoings v income.
Quality of life is important, so making a way to get the right house for the family will add a lot.