[CHAT] Framing question

I'm fed up with having a load of finished pieces sitting in a drawer because nothing fits a standard frame and I don't feel like selling my kidney to afford a 'proper' frame. So I'm thinking of working backwards on my next piece - I know the size of the pattern, I want to find the size of the nearest 'standard' frame and then from there work out what material size I need.

So I'm thinking of doing (well, getting the pattern for christmas!) the Peppermint Purple uk blackwork (https://peppermintpurple.com/products/uk-eire-counties-blackwork?\_pos=1&\_sid=f03d72412&\_ss=r)
I really like how they've framed it.... On size 14 it says it'll be 35 x 45cm in size. But when I look for frames it seems that to have the mat included you need to jump up to 50 x 70cm and then the mat has thicker top and bottom than sides. I really like the way Peppermint Purple has it in their pic - the same thickness mat all the way around.

Am I being a total numpty and my google ability has fled? I know this is just mocked up for a pic, but this happens EVERY time I try to buy a standard 'off the shelf' frame. Does anyone have any hacks? Secret websites that sell frames with even matting? Cunning ways of cutting the matting down bearing in mind it often has a bevelled edge?

Bonus points for any links that include shipping to Australia! Thanks all