My mum was very round shouldered and had to tie a piece of tape between the back of the straps to hold them on her shoulders.
Yeh, Accymel, know what you mean about body change ... was 34B for years and years, now find 34D ! .. when did that happen ? Still a 10 sometimes 8 jackets on the shoulders, but fastenings can pull a little .. blouses gaping, etc.
The measuring services are reasonable good, but have learnt always best to try them on before buying .. pain in the backside, but well worth it.
I love all the colours that are available now and the way it doesn't matter anymore if the straps show under a strappy dress/top; hate those clear plastic straps.