Hi, PurpleMolly!
I have used bubble wrap before in my mold. I think it turned out well:
These bars are a goat's milk base that I added honey and ground oatmeal to. Oatmeal, Milk, and Honey F.O.
I used a regular four-cavity bar mold, not a loaf mold, but I think you could do the same with a loaf mold. I just lined one side, the inside of the mold with the textured side up. To "glue" the bubble wrap to the mold, I just put a tiny bit of soap base into the mold and swished it around to just cover most of the bottom before pressing the bubble wrap into the mold. I let that dry a few minutes, then I poured the base over it (make sure your base isn't too hot) and took a toothpick or craft stick (or a spoon or something like that for a bigger mold) to push along the bottom and sides to work any air bubbles to the surface. Spritz with rubbing alcohol to burst surface bubbles, and you're done!
It's fairly easy to pull the bubble wrap away. I find it's easier if you leave a bit of overhang off the sides of the mold so you have something to grab a hold of when it comes time to unmold.
For F.O. usage rates, .25 oz. per pound is a good rule of thumb. Fragrance is a personal thing; some use more, some use less. Personally, in general, I use about 2 tsp of F.O. per pound (16 oz.) of base.
Hope that helps! Have fun!