A;most done with my 70's, so take this with a grain of salt.
There are string trimmer attachments that support the heavy end of the trimmer on two wheels. The whole assembly is still light weight and easy to move around. If you are mowing downhill into a ditch, and then pulling back over and over, you might find a string trimmer on wheels is easier to use.
There are battery operated trimmers and 4-stroke trimmers, and corded trimmers, so you have a wide selection.
I have not seen the trimmer wheel attachment in stores, but there are plastic and metal versions available on aliiexpress for less than $20US.
My old Poulan Weed Eater must weigh over 30 lbs, and I have to use the shoulder strap to use for more than a few minutes. Newer models are a lot lighter and easier to maneuver.
Unless you want manicured level, that should do the job, and the wheel attachment would help with moving, and tend to keep the cutting pretty level.
tom
an example (search for string trimmer wheel attachment):
Buy Adjustable String Trimmer Support Wheel Attachment,Lawn Mower Auxiliary Wheel,Push Behind Weed Trimmer for String Trimmer Weedeaters Grass Cutter Brush Cutter Garden - Black at Walmart.com
www.walmart.com