Well, I found the roll of fusible stretch tape that I was looking for. And after a few snips here and there to remove the bias mess I made of the neckline. I then trimmed and reshaped the armhole and neckline before fusing the bias fusible strips. It worked better than I hoped it would.
The fusible tape gave the fabric the structure that it needed to be folded over and top-stitched creating a nice clean finish. I also used it on the bottom hem. For the straps, I used some vintage bronze coloured bias tape from Mama R's stash. Seriously, it must have originated from the seventies. But it worked perfectly with this fabric.
And the best part, Mama R is over-the-moon with her new slip.
Fabric: 1.2 metres knit lace
Knit Bias Tape: 2 metres
Fusible Tape: 3.2 metres
Bias Tape: 1 metre
Pattern: Burda Style 6964
Additional Tools & Supplies: Janome sewing machine and serger, new sewing machine needle, walking foot, scissors, thread clippers, pins, cutting table, iron, ironing board, time to sleep on it and figure out my next move, coffee, and breaks here and there.