I can't say whether or not you'll fit back into your old clothes. I know my body now, and I know what it would take me to lose 10-20 pounds.
I have fought my weight for 3/4 of my life. I know your pain.
I have never had the kinds of designer items you do, so clearly, my experience is very different.
The few times in my life I have successfully battled and won required a commitment I probably won't ever have again. At one point in my life, I got down to a size 4 and wasn't happy because I wanted to be a size 0. Another story, but yes, i was once thin.
My most recent weigh battle has been after having two babies and many miscarriages. My body is not young, taunt and smooth. It never will be again. I may not ever get back into straight sizes again on my bottom half. I want yo say I am okay with it, but it's a struggle.
I boxed up everything that doesn't fit and stored it in the basement. I checked back in spring to see if anything fit and again in summer. I will do the same thing this fall, winter and next spring and summer. If it doesn't fit by next summer, it's gone. I will donate it all to either dress for success in the case of my suits or to my church.
Life is too short. My body may not meet the young, toned, smooth, and thin definition of beauty that our culture is obsessed with. But it's mine, and I will take good care of it and dress it to the best of my abilities whatever it's size and shape right now. It does most of what I ask it to, and I am fortunate to have my health and my daughters. Rather than view it as the enemy, I try very hard to treat it as a friend and never think or say anything about it I wouldn't say about a friend.