Mortgage affordability

Hi, just wanted to see what people think. 46m and 43f with one child (going to private school). Thinking of upgrading our house to a forever home. Total household income just over 200k and starting 30-40k annual in private work (limited company do tied up). Have decent savings of 300k in ISA. DB pension. Is it a good idea to take mortgage of between 400k-450k at our age. House just under a million. Child may get entry into grammer but if not private will cost about 25k in secondary. The mortgage 20 years with 4.8% is just under 3k per month. Thanks