How about the B&R Baseline International Carry On? I have linked the John Lewis site as I can see you are in the UK.

It's listed as 43L capacity which isn't too far from what you have, it also looks big inside compared to my Rimowa Salsa Cabin.

It is only a few cm's over the AF and FR dimensions, unless you are on a packed flight you shouldn't have a problem, the sizer in my experience is slightly bigger than the dimensions.

I don't want to be one of those posters but for 5 days away a cabin size case should easily have enough room. As well as you list i would have room for gym kit and laptop, notebook, chargers etc. Why would you need 4 t-shirts? Perhaps look at your packing to ensure maximum use of space.

From my experience when using something that has served well and is no longer on sale it is a case of weighing up the options and then taking the plunge.