You are not necessarily looking at a Workstation but you could be looking at a significant expense.
Arranger software is available, I am not talking about a DAW but an awareness that other forms of software is available and this may be one course of action for you to research.
The ability to switch sounds seamlessly is generally not possible in low cost workstation keyboard eg in a Korg Kross 2, but a Roland FA can do it to an extent but these are not Arrangers.
Take a look at what a Korg Pa700 or Yamaha PSR SX700 can do, and I can tell you that with the Korg it is possible but your use of a sustain pedal and timing is the key to making the transition as seamless as possible.
Watch this starter tutorial and then work your way through the rest of the series and you will then have a good understanding of the capabilities of a mid range Arranger