Another vote for tires..they can make a world of difference. A couple bikes I've purchased had "tires" on them that made road riding feel like I was riding in soft sand. New, fast, easy rolling, lightweight, supple (pick a descriptor) tires made them feel like a new-different bike.
Of course, you want decent flat protection too, but you can get both.
Some specific suggestions(tire mfg make many types within a model-line of tires, it's easy to buy the right model tire and still get the wrong variant within that model):
>>Schwalbe Big Ben HS 439: they seem to make a 700x38. Get the Raceguard model (not K-Gaurd, or Big Ben Plus), their model# is
11100564. I run Big Bens on my tour bike in 26x50. Cushy, easy rolling tires..love them. https://www.schwalbetires.com/bike_t..._tires/big_ben
>>Schwalbe Big Apple HS 430: This is a lighter weight version of the Big Ben (or, more accurately maybe, the Big Ben is a more robust version of the original Big Apple). They make 622 x 50 version..though it'll be heavier than the BB above.
>>Schwalbe Marathon Supreme HS 469: I've not run these..yet..but folks seem to love them. I'm becoming a fan of Schwalbe tires. I'd like to try these. Looks like they make a 700x40. Schwalbe rates these as not so great off road (the BB above are quite good there). I ran some Vittoria Hypers that had a tread similar to the Supremes..on road..wonderful tires(I wish they still made them)..on damp-wet rail trails..bad. https://www.schwalbetires.com/bike_t...rathon_supreme
>>Schwalbe Marathon Almotion HS 453: Another well-loved tire I'd like to try. https://www.schwalbetires.com/bike_t...athon_Almotion
>>Panaracer Gravel King slicks: I run these on several of my bikes, my GF runs them on her touring bike..fast road tire, good on light trails/gravel, lightweight, no issues with flats. There's lots of new models in the "GK" lineup lately..be sure you get the right ones (not the SK or Plus versions)
https://www.thebikesmiths.com/collec...31278478032960
>>Panaracer GK SS: Looks like there's a new SS version that is between the slick and SK..might be a good candidate for touring. They also come in a larger 700x43. Appears to be a very nice tire. The SK(small knob) version(surprisingly!) runs pretty fast on the road(in my experience)..I'd guess the SS version should be about the same as the slick version.
https://www.thebikesmiths.com/collec...35638826827936
The best sources I've found for the Schwalbe tires are Bike24 in Germany & Bikesmiths in Milwaukee for Gravelkings.