Bells

[rosiegreengrass]

All answers contain the word BELL, which may be part of a longer word.
1, Settled and comfortable era after WW1(5,6)
2, Not used as a fastener (11)
3,A blissful sound? (7,5)
4,French writings of a literary nature (6,7)

[boxtops]

3 Wedding bells

[sandyRoe]

4 Belle Lettres

[Bummle]

4 belles lettres

[sandyRoe]

Belles Lettres^^^

[plautus]

1 Belle Epoque, except it was the period BEFORE WWI

[boxtops]

1 Belle Epoque

[boxtops]

I agree with you, Plautus - this clue could be a misunderstanding - wiki says "The Belle Époque was named in retrospect, when it began to be considered a "golden age" when compared to the horrors of World War I."

[Prudie]

1 Belle Epoque ? Although I thought that was until WW1 not after

[guilliebrougues]

2. Bellbottoms (as in trousers)

[Calibax]

2 Bellybutton