I'm sure this is familiar to a number of people on this forum...

How do you book paid upgrades (above and beyond your companies travel policy or budget)? For tier points, personal sleep comfort, etc.

Often times, upgrading separately after booking incurs change fees and availability might be different. So there's an incentive to book into the preferred class of travel from the start.

Given businesses need invoices of exact amounts paid, offering to pay the difference through a different payment method, buying yourself and then expensing, or deduct from salary can get tricky since you muddy the exact amount the business is spending.

What do you do?