I agree with Anya and missvee!
I've lost over a hundred pounds in the past few years, and you know what? Waiting to wear nice clothes actually had the effect of slowing down the process. I still have more pounds I'd like to lose, but I've really noticed that when I feel good in my clothes, it's *easier* to stick to my food plan.
Furthermore - I have done that thing where I've bought something a size smaller, or held onto something that was too small - it never works. I held onto a beautiful dress that my Mom had bought me years ago...was so looking foward to being able to fit into it again. Hmmph - I completely missed my chance. By the time I remembered to try it on again, it was too big.
With buying a pair of pants or something a size down (did that too), thinking I'd fit into them in mere weeks, somehow even though I did eventually "fit into" them, they didn't look right. You don't always know what your shape is going to be like a size or two down. What looks flattering (even if it's too small for now) might not be when you fit into it.
Personally, I'd order the next size up to try on - it could be that it's too big. That happens too - being in between sizes. It'll all depend on the brand. If it fits and you love it, then I think you should get it. <--sorry for being a total enabler
One last thing - going down sizes also depends on where you're starting from. When I started out losing weight (wearing a plus size 3X), it took a good 20+ pounds to drop a size. These days (size 8-10), if I drop five pounds or so, I go down another size. This might help you decide whether to get the leather jacket now, or wait.
It's not going to hurt to try on the larger size, and Nordstrom is very good about returns. I wouldn't recommend buying something that doesn't "quite" fit - in my experience, when I did this, the item didn't always look as good as I thought it would by the time it did fit. This is especially true for things like jackets, coats, tailored dresses and slacks. I was ok with buying smaller sizes of things like sweaters and even jeans in most cases.
Looking forward to hearing what you decide.