I think you meant disk space as 128GB of memory is possible but expensive in laptops. I have yet to see 256GB in laptop form but it is possible.

As to 8 hours to reach that under all use you need a laptop that starts at 80 hours. Why? Because actual use time varies about 10X from max to min. There are no 80 hour laptops today.

In your case you may need to shop 16 hours for your use to hit 8 hours.

That all out of the way CNET always liked the Dell model I'll link to next.
https://www.cnet.com/products/dell-xps-13-non-touch-2015/ Yes, you have to look at this years models but non-touch and a plain display do help in battery time.

-> Another issue with battery time is that it drops over the years. So if you demand 8 hours you are shopping a 32 hour model because use cuts the time in half and in 2 years the battery wear takes it in half again.