I’ve been flying abroad for work throughout the whole thing. ExpressTest at the airports have been my go-to, I’ve never had a test result take more than 24hrs and it’s usually much earlier than that – I tend to get a test later on in the day, have had results back that evening or first thing the following morning.
On the 48hr thing I’d double check the requirements. For flying the test result just has to be valid at the time of departure, not the time of arrival in the end country.
When it comes time to return, good luck. I’m in Scotland so we have a single choice for the isolation tests, they turn up when ordered and results are next day. The guys who live in England haven’t had such a smooth time of it: tests undelivered, results missing, etc. My own experience of flying back to England once was the same, test booked but never turned up.