Suggest you consider a new Tiagra level crankset and bottom bracket, same arm size, now on sale for around $105 at Performance Bike: Shimano Tiagra R460 Crankset (Black) (2 x 10 Speed) (Hollowtech II) (175mm) (48/34T) - Performance Bicycle (performancebike.com)
That will make a significant difference.
However, while changing the crank, you might as well go further and replace the cassette and chain. SRAM makes a fine cassette in 12/28 (note that your freehub may not accept an 11 tooth small cog as your bike was produced during a period when not many bikes used them) and while Performance sells them for $78, you might be able to find a better price elsewhere: SRAM PG-1050 Cassette (Silver) (10 Speed) (Shimano HG) (11-32T) - Performance Bicycle (performancebike.com)

SRAM also makes my preferred chain, which Performance has for $7.50: SRAM PC-830 Chain (Silver) (6-8 Speed) (114 Links) - Performance Bicycle (performancebike.com)

The RD on your bike can absolutely handle a 28 tooth large cog. So, using this example, for around $200 you can keep the bike that fits you so well AND have the gearing you need. It's the same gearing I use on many of my own bikes (and I'm 72). I'm only using these examples from Performance because they were easy to find.

Questions? Just keep asking. Lots of good advice here.