Thisbodice thingy is from a pattern (Burda #7876), comprised of ~9 panels around. It was a bit confusing for my little brain, but it worked out in the end.
The front closures are actually snaps... buttons are just for show.
The straps meet in centre of back panel.
I recycled the fabric from a pair of stretchy 'dress pants' that no longer fit.
The contrasting side panels are linen upholstery fabric.