Can you change the entrance in the small ensuite to service the back bedroom; then convert the small bedroom into an ensuite for the master bedroom? If you move the wall on that room right out to the door of the master bed you'll gain, in guessing, 300mm. Ensuite at 2m*2m would be large enough, you'd then have the space for a narrow walk in wardrobe 2m*1.2m, giving a walking space 7/800mm wide, just big enough. To get natural light in the you could put glass in part of the partition walls up high, both at landing side and ensuite side.
Alternatively, make small room into a jack and Jill, big saving on cleaning and make old ensuite into wardrobe.

Thanks for your suggestions. That was my original idea to use the ensuite in the master for the back bedroom and convert the small bedroom into new ensuite for master bedroom. Good to hear my thoughts make sense.