My beds are 5ft across, a bit too wide in reality & not raised. Because hubby used to them & needed the width to make it viable. Now I do no dig I’m considering making them narrow but I have slabbed paths in between but might in time remove them (just don’t tell hubby or my children this , as they shifted them all from various places to the plot lol). For me 3-4 ft would probably be wide enough as I’m only 5ft 2”.
I would add a caution here & say do you really need raised beds? I used to think that was the way to go as that’s what lots of tv programs suggest, but if you’re soil is good & you have good drainage,they aren’t always the best-the soil can dry out very quickly, they take a lot of filling, the wood rots, it’s time consuming to build & fill them. Slugs love to hide down next to the Wood & come out to feast on your plants at night.