There are a few different versions. One made by Medela looks like this: https://www.medelabreastfeedingus.com/products/51/supplemental-nursing-system-sns
They also make one for short-term use (but I've heard of people successfully using it for several months -- just keep it very clean): https://www.medelabreastfeedingus.com/products/52/starter-supplemental-nursing-system-sns
Then there's the Lact-Aid: https://www.lact-aid.com/trainer-systems/
I wouldn't invest in anything other than the starter SNS unless it becomes apparent you're going to need to supplement long term (which likely won't be the case).
You can also make your own just by putting a feeding tube into a bottle of supplement. Then latch baby on to your breast with the tube in his mouth (or latch him and then slide the tube in) and he'll nurse and provide stimulation to your breast (stimulation = better milk supply when mature milk comes in) and get the supplement at the same time. It will look something like this (a video of Dr. Jack Newman, IBCLC, showing how to use one): https://www.youtube.com/watch?v=ezGIkIkhC_o
I believe that a hospital nurse could round up a 5 french size feeding tube if you ask for one.
A pediatrician we saw early own poo-pooed nipple confusion so we supplemented with a bottle. A week later, my daughter refused to nurse. It's true some babies go back and forth totally fine. But it's also true that some don't and you won't know which yours is until the mess has been created.
How many wet diapers were they expecting him to have in the first 24 hours anyway? I thought it was 1! 1 wet and 1 dirty diaper per day of life in the early days (first 3-4).
https://kellymom.com/bf/normal/newborn-nursing/
I love looking at the beautiful little babies... helps to pass the frustration while waiting for my own to show up!
Can't wait to hear your LO has arrived... maybe mine will feel shamed that yours got here so much sooner and decide he better hurry up too!
But Ben is here safe and sound now! 
