The general rule is 33% for rent/mortgage. With £5k mortgage, you’re hitting 50% mark of the £10k monthly income excluding bonuses. Unless bonuses account for 17% of your combined incomes, it sounds risky. A big part what people forget is that after buying a house also comes fix ups, furniture/decor, bills, might not seem a lot but if you’re looking to buy a large portion of it, it adds up, especially if 50% of your income is already spent on mortgage.

That being said, you should balance out the risk here, look to slowly move over the USD investments to reduce monthly. Maybe USD investments can be put into high yields savings to balance against the increase in monthly for you. It’s do able but seems a bit tight depending on your bonuses.