Victoria Blazer Fitting Problems: Help needed!

While my September summer vacation feels like forever ago, I still remember that sad feeling when realizing I have to put my beautiful sandals on a shelf for another 8-9 months. It’s the worst. The good thing: Rainy autumn days are perfect for sewing! Yay! One of the projects I’m most excited about finishing is my Victoria blazer in the most awesome colourful fabric.

There’s only one problem: This project is giving me a headache with some fitting issues that I am not able to figure out on my own. So guys, I need your help. Maybe some of you have an idea how to address these problems?

I’m not in a rush, so if someone reads this post months later and has any idea, please let me know.
Here are all the details:
Victoria Blazer Back Fitting Problem

Main Fitting Problem: The Back

The blazer sticks out weirdly in the back. I know it is not supposed to be very close fitted there and I also have a sway back, but I still think it is too much. As you can see in the photos, the fabric creates an outside curve when – in my opinion – it should be hanging at least straight.

The body of the blazer is underlined with cotton batiste. Could that be too stiff? The lower front sticks out a bit too, but I can live with that. The back is the main thing that bothers me. I’m just confused whether these problems are fitting or fabric related.

Victoria Blazer Back and Sleeves Fitting Problems 1

Fitting Issues: Sleeves

Also the sleeves – which are underlined in cotton voile – show a big wrinkle in the back shoulder area. Could this be because of my forward shoulder joints or is this related to the fitting issues in the back?
Victoria Blazer Lapels Fitting Problems

Other Issues: Lapels

The lapels in the front also stick out a bit. I already tried to fix this by the magical powers of pressing (you know, tailor’s clapper and all), which helped a teeny tiny bit. But they still look weird. They’re in the same cotton batiste I used for underlining the body. And they’re interfaced. Maybe that is too much and a softer, uninterfaced fabric would solve the problem?
Victoria Blazer Mexican Fabric Detail

Victoria Blazer Fabric Detail 2

Pattern and Fabric

This is size 4 of the By Hand London Victoria Blazer. The fabric is a colourful woven fabric with a bit of body. Maybe a little heavier than chambray. It has a bit of drape, so I thought it would be enough for this pattern. The fabric is rather loosely woven so I was afraid my elbows would rub through the sleeve after some wear. Therefore, both sleeves are underlined in cotton voile. The body is underlined in cotton batiste which is also the fabric I used for the lapels.

Known fitting issues on my body

Fitting issues that I already know about are my forward shoulder joints, my rounded upper back and my sway back.

I hope, I was able to describe everything in an understandable way. I tried my best.

Most of all, I don’t know where to start fixing these issues. Take in the back at the sides? Underline the body in a different fabric? Make a muslin, adjust and go from there? Try again, hoping for the best?

I’d love to know a second opinion on this, so if any of you have the slightest idea , I’m all ears.
Thank you so much!