Try a traditional swept bar -- albatross, North Roads, etc. There's a pretty good reason why those were popular for decades. They work.
My old Univega MTB-lite has morphed from the original flat bar to lower riser bar to albatross bar. The swept bar is a keeper -- comfortable, versatile with almost as many hand positions as a drop bar. And the brakes and bar-end shifters are accessible from most of those hand positions. Leaning into the forward arc of a swept bar feels like riding the hoods on a touring type drop bar bike. Some folks prefer mustache bars with the brake levers in that position.
Flat bars are great for quick maneuvering at slow to moderate speed. But they aren't comfortable for long rides. By the time I realized I was considering bar-end grips to make a flat bar more comfortable, it was because I wasn't using the bike as it was originally intended. If I was riding 2 hours or longer at a time, 30-60 miles at a time, I was ready to try handlebars better suited to how I rode the bike.
The only problem with swept bars is they can hinder tight turns if the ends of the bars knock our knees, thighs or top tube. I rarely encounter that problem, probably because my bike has a long top tube and stem so the reach is pretty long. Swept bar ends can be trimmed if needed. But add-ons to flat bars might be better for folks who still need the maneuverability.