I agree with @Navmaxlp - get the Godox TT350P. Like the Metz, it's light-weight, compact and affordable and useful for outdoor fill-flash. The crucial difference for your requirements is that the Godox has tilt and swivel: that is, the head twists around to point in almost any direction. The Metz can only tilt up and down. Tilt and swivel gives you the ability to bounce the flash beam off the walls (or some other surface) and not just off the ceiling, which is crucial to getting a softer, more diffused, light on the subject. The Godox also has a higher maximum output (which means, amongst other things, that you can bounce in a bigger room) and a number of features that you might use as you develop your flash skills (like HSS, manual control and built-in wireless for off-camera use with an XProP or another Godox flash).
Honestly just the simple expedient of bouncing the flash from more surfaces will make a big difference to the quality of the exposure. Have a look at these articles from Neil van Niekerk:
Bounce flash photography tutorial bounce flash photography - be bold! How to bounce your flash
In this video, van Niekerk tests a lot of diffusers for an indoor on-camera flash. The best results? No diffuser, just bouncing the bare flash pointed behind him.
Better still, use directional bounced flash with a flag (like the flag that @mcgregni demonstrates in the page linked above). Van Niekerk demonstrates this with his "Black Foamie Thing" (a piece of black card strapped to the flash) in the last couple of minutes of the video.