I think you'd be good with most any 3M reflective sheeting product. In general, white is the most reflective - the colored sheeting/tapes are less reflective. eBay and Amazon are good places to shop for this stuff. Most of the 3M product is sold in large rolls that cost $xxx-xxxx.

IMO, any reflective material is but a secondary safety measure to the necessary primaries - head and taillights. It's a good idea to run 2 taillights, in case one quits or falls off. I always mount my main taillight just below saddle, then another on the back of helmet (you'll have to jury-rig a mount with zip ties). Wearing white shirts helps too (lots of area). Or go full safety nerd with a safety vest. I have this one, it's real 3M Scotchlite and highly reflective. Many of the chinese safety vests barely reflect - they cheap out on the most critical component.