World champion Josh Kerr will join fellow Scot Gourley and Mills in the 1500m team.
Already assured of his place in Paris, Kerr chose to race over 800m in Manchester and fell in the final straight after a heavy collision with Elliot Giles.
Jake Wightman, the 2022 world champion over 1500m, was granted a medical exemption after pulling out with a “minor” calf injury.
With Ben Pattison and Max Burgin finishing first and second in the 800m, Wightman must hope for a discretionary place in the event he won a European silver medal in two years ago.
Laura Muir ensured she will be competing at a third Olympics but had to dig deep to finish second over 1500m.
The silver medallist from Tokyo in 2021 was well beaten in a sprint finish by Georgia Bell.
Jemma Reekie was also second in the 800m, behind 17-year-old rising star Phoebe Gill.
Those two will join Olympic and world silver medallist Keely Hodgkinson at the Games.
On Saturday, discus thrower Nick Percy clinched his Team GB place after finishing runner-up to Chukwuemeka Osammor.