To Outlive Eternity and Other Stories (2007) - a collection of longer works by Poul Anderson. The title novella (a 2-part serial in Galaxy in 1967) was expanded into the novel Tau Zero. I was somewhat disappointed with the novel version, but think the original version might be preferable - the concept is compelling. After Doomsday was also a 2-part serial in Galaxy (in 1962) - later a slim paperback. I doubt it will ever appear in hardcover, so this is probably your best option for a "deluxe" version. Anderson was prolific with a long carreer, so the rest have appeared in one or more Anderson collections - often in (mass-market sized) paperbacks. I'll recommend "No Truce with Kings" and "Progress."

To Outlive Eternity
No Truce with Kings
Progress
Un-Man
The Big Rain
After Doomsday
Epilogue

These originally appeared from 1953 to 1967 - (2) in Galaxy, (2) in Magazine of F&SF, (2) in Astounding; and one from Analog.