I would like to turn my Fisherman's Apron into a Fisherman's Smock. Is there a chance of losing the item? What would be the best way to go about this, somehow attempt it myself or shout for help? I'm really new to synergy, so I'm not sure where to start.
You can never lose the synergy ingredients due to a failed synergy attempt. When the attempt fails, you click on the furnace again, and all of your materials will be returned to you. If you don't have room in your pack for it (which can happen with multiples of the same stackable ingredient, because the game insists on you having space for all of them unstacked), the game will tell you to sort your inventory and make space.
There's no time limit to retrieve your materials either. It doesn't even have to be retrieved at the same furnace, AFAIK. I took a long break from skilling up Synergy. And when I started up again recently, I was surprised to find some ingredients that I had left in there months ago.
It takes synergy skill in the mid 40s to be able to successfully create a Fisherman's Smock, you will either need to skill up synergy or find someone with sufficiently high synergy skill. Either way, you will still need to do the quest to obtain a synergy crucible ("Synergistic Pursuits"), which is what allows you to claim the use of a furnace.
As long as you have the crucible key item, someone else can do all the work. You just have to be the one who starts the process by claiming the furnace, and then add all the materials (which in this case is just the Apron). After that, anyone who is in your party can perform the synergy operations for you.
Check out the wiki resource on Synergy. You may find it useful. http://wiki.ffxiclopedia.org/wiki/Category:Synergy