No doubt that a single breasted fly front mac makes for a much cleaner profile and is more in keeping with an Ivy look.

But the double breasted trench raincoat is a classic piece that’s been around for over a century and if you’re going to have one make it a Burberry’s (not Burberry) for goodness sake. Sure its fussy, the belt that you can’t quite figure out what’s the best way to fasten, the epaulettes, the D rings, the vent, the storm flap, the liner with its annoying tendency to come unbuttoned, but they’re all details to revel in. It’s a statement piece, like a polo coat, one to be taken out on a rough day and worn with panache. On a practical note if you’re walking into the wind and rain you have double protection with the double breast cut, you can really batten the hatches down in a proper trench coat and laugh at bad weather.

Do your research, find out what size fits you and hunt around for a good vintage one. Fakes abound. They’ve screwed with the design on new ones even if you did want to shell out the £1500+ they are asking.

I once owned two Burberrys' BTW, the first purchased for £1 in around 1996, the second for a few pounds a few years later.  The first had ended up on a sail rail in Help The Aged (or somewhere similar: the shop still exists), so I happily wore it with cords and Loake brogues until I outgrew it. 
My ancient fly-fronted was a £30 Ebay bargain in 2010.  John Simons reckoned it to be a one-off from around 1967.  It has a tartan blanket lining.  It ensures me a reduction whenever I want to take a piss in Ashby-De-La-Zouche (a fine town) and found me refused entry to a homeless centre.