Alterations Issues

I bought a beautiful dress and planned to have sleeves added to it. Last time the sleeves were made, and it looks beautiful but the because of the weight of the dress and as its mostly backless the sleeves kept slipping off my shoulders. Obviously they plan to try to fix this (the netting on the bust was a bit big which was
part the problem) but I’m worried this isn’t the only issue and that the part that covers the shoulders is too ‘drop shoulder’ style and will continue to slip.

Part of my issue is I’m finding it really hard to communicate with the seamstress...she is lovely and experienced but I feel like when I try to mention something she thinks I’m being a total bridezilla and worrying about nothing. I have no family where I live (my family literally lives 12,000 miles away from me in New Zealand) and no friends to come and help as I moved here not too long ago to be with FH. I feel like my communication issues could be solved if I felt like I had a bit more knowledge around the altering. Does anyone know of any way to stop sleeves falling off the shoulder in a backless gown? I can’t pin it to a bra as the bra is in built (any other bras all showed either at the back or through the dip at the front). The only idea I’ve had so far is to bring along some double sided tape on the day just in case lol though I don’t know how well this would work. Any input would be appreciated!