If you have your own business, you have the opportunity to have the business make the contributions to your pension, rather than paying them yourself out of your earned income.
Although you get tax relief either way, when the pension payments are made by the business, they do not appear on your payslip, so there is neither employer nor employee National Insurance to pay.
Depending on your earnings, this may be around 25% of the gross, so is a big saving.
Company employees can sometimes do the same, if the employer agrees, calling it "salary sacrifice"
If you want to maximise your taxable salary, to increase the mortgage you can get, I suggest pausing or reducing your pension contributions temporarily, then making them towards the end of the tax year, when you have calculated your profits and decide what you can afford.
Annoyingly, when I used to make contributions from the company account, HMRC accused me of claiming the personal tax rebate, as if they had come from my own taxed earnings out of my own account. This was not true, as I could easily show, but the company who did my payroll (accountants often offer this service) was dragged into an investigation which caused them additional work and expense, and this led them to refuse to continue it. Once HMRC have you down as a suspect they can make your life a misery.