I'd go with something wider that 7cm - otherwise you might need to double-tape thicker parts, like the downtube. If you are only looking to wrap the chainstay or fork, you might be ok.
For my first bike (wasn't used to ordering stuff from AE yet), I went with a premium car vinyl. And also because I wanted a matt one, since my bike coating was matt as well:
https://luxshield.de/Lackschutzfolie-Transparent-matt-15x200cmMust say, even though it was a bit pricey (35€ for 15x200cm roll), it was well worth it. I covered my whole bike frame with it (~90%) - not just the downtube and chainstay. On the bike it is basically invisible from more than 30cm distance. And even if you look at it closely, you have to know it is there or just happen to look at an cut line/end of it. It's still in the same condition one year later, even after a many winter rides, lots of mud, and a few pressure washes. No corners started to peel either.
The also offer "pre-cut vinyl" for bikes but that was even pricier. However, might be worth it, as the measuring, planning, and cutting all the parts took quite a while.
For my road bike I just wanted to cover the downtube and chainstay. Wanted to try a cheap alternative, so gave this one a try (~2€ for 15x200cm):
https://www.aliexpress.com/item/1005005677268215.htmlCompared to the premium brand, this one is a bit harder to cut and apply. It might be a bit thicker or just cheaper material. Even though, it was still rather easy to cut to size. But I didn't have any "complicated" shapes this time as downtube and chainstay basically meant two rather regular rectangles.
Even though it is not stated in the product description, you can also apply it wet, which makes it even easier to avoid air bubbles or dust containment. However, since it was less bendy than the premium one, it took much longer to adhere to the shape. Wasn't an issue on the downtube as the two bends are rather big but on the chainstay, I had to "babysit" the adherence for about 30 min. Might be different, if you apply it dry but would recommend the wet application nevertheless for much cleaner results.
This one is almost just as invisible as the premium one. However, even after a few months, the corners on the chainstay started to peel off a little. It's mostly on the inside, so not a big concern but I might want to re-apply it after the winter season to have it look nice again. The downtube is just fine.
