Your current low gear ration is 1.7:1. Most likely, your rear derailleur will handle a 13/28 cassette with no problem. That gives you a low of 1.4:1. I don't know what the hills in your neighborhood are like, but if you have long or steep, you're probably looking for something lower. Consider this phase one.

The least expensive phase 2 would be to purchase a compact crankset with 50/34t chainrings. You might need a new bottom bracket, too, but this is no big deal. This would allow you to use your current shifters, derailleurs and cassettes. The smaller chainrings would give you a low of 1.2:1. Unless your doing 1500 ft. climbs, this might be sufficient. Shimano Claris would fit the bill.

Phase 3 would involve shifters, crankset, cassette, and derailleurs, either a 2x10 compact double or 3x10 triple. Compact double would give you 50/34 up front and 11/34 in back, for a final low ratio of 1:1, a little more on the top end, and some closer steps in the middle. I recommend Tiagra 4700. the triple setup would give you 50/39/30 up front and 11/32 in back for a final low ratio of 0.9:1. I'd choose Tiagra 4703 for this.

I chose 10-speed cassettes because 11 or more would require a new rear wheel, upgrading to 9 wouldn't be worth the bother, and Shimano Tiagra 4700/4703 is really slick stuff. I guess you could also go Claris 3x8, but you're still going to need at least a new front lever and derailleur. I wouldn't bother. And if you're replacing the cassette, a new chain goes without saying.