A standard bath is 1700mm long, Jj. A 1700mm "walk-in" shower tray should be ideal.
Glass doors and screens combined are available for these.
A plumber would have to look to see how the waste pipe runs, and how it's connected to the drainage.
A tray is a lot lower than a bath waste. In fact, for a proper "walk-in", the waste usually has to run BELOW the floor.
Often quite possible, but you'd have to actually be there to see if this were possible.
I think it's a great idea Jj. You wouldn't regret it.
Don't fixate over the existing tiling though. Some extra tiling is well worth it.