Yes, having a Comfort+ seat will bump you up in the boarding order (to Zone 3). Getting a DL Amex card (Gold+) will also bump you up (to Zone 5).
See - https://www.delta.com/us/en/check-in...rding-priority
Not aware of other options to simply pay for a higher boarding Zone number at this point.

Comfort+ seats are a different beast on Delta compared to AA as Delta actually sells them as separate fare classes (W and S). I can't really say much about upgrade offer pricing (online seat upgrades) for Comfort+ on this route, but I can tell you from ExpertFlyer that if you go the upfare route (simply paying fare difference from Main to C+ fares), the fare difference will either be $70 (W class) or $50 (if there is S class inventory) each way. There seem to be quite a few routes where DL seems to rarely open up S class inventory on flights and this looks like it may just be one of those routes so you are probably looking at the higher $70 each-way price in most cases to upfare.

There is a technique where you make a temporary booking on a route to get an idea of the online seat upgrade offers on that route and if they are cheaper than simply paying the fare difference. This is because you have until midnight the next day to cancel a DL booking and get a full refund. Note that the offers are dynamic and just because you are seeing a cheaper offer than the upfare pricing doesn't mean that will always be the case.