Help with Daytime Journey on Side Upper Berth

Hi all, I have a daytime journey coming up, and my seat is the side upper berth in a sleeper train. This is my second time traveling in a sleeper class and my first time traveling solo, so I’m a bit nervous.

I’m unsure about the rules for sitting during the day. Is it okay to sit on someone’s side lower berth during the day if I have the side upper seat, or is that against the rules/etiquette? I’m not very comfortable climbing to the upper berth (I’m overweight), and I’m not sure how to handle this situation without causing any issues.

I’ve seen posts here where people mention that passengers guard their side lower seats fiercely, and I’m not a confrontational person. I don’t want to cause any issues.

If sitting below isn’t an option, does anyone have tips for making it easier to climb up to the side upper berth?

Thanks for your advice!