To keep the electronics secure in the knit outfit, a 5 inch square bag (5" x 10" of cloth) is fashioned. Velcro was used to seal up the top and bottom. The LiPo is the heaviest part - to support the parts and protect the wearer, a small inner bag was sewn in. The Flora on/off switch is accessible from the opening at the bottom of the picture while the speaker, IR sensor, and Neopixel are fed out the opposite end into the outfit. The loopy side of the velcro is sewn to hold the bag to the knit outfit with a zigzag stitch.
Here is the completed project and a close-up of the Neopixel at the top and the IR sensor in the center of the black band (blending in).
And here is an English Toy Spaniel ("Spidey") wearing the costume:
And video with the sound effects (Spidey was fairly tolerant of the sound after becoming a bit familiar with it but it did help to be able to turn it off after a bit):