Clawed

Much of the conversation here has been about the difference between men's and women's pelvis and fitting a seat, when the OP was very specific that her problem was her coccyx, her tailbone. I am not sure there is much gender difference with tailbones, but there can be some pretty extreme variations between individuals.

Think of your lower spine and coccyx like the palm of your hand. The heel of your hand is at your lower back and your fingers project forward between your legs. The more your hand is cupped, the more the coccyx is curled upward in the body. The straighter your fingers and palm are, the more nearly flat, the more the coccyx swings down out of the body, and the more it is exposed to the surface you are sitting. This is all within the normal range of variation. If the OP has her coccyx more downward pointing the more I would expect it to impinge on the back of the seat and cause pain.

She might try some of the saddles that consist of two pads that are pivoted and have no forward horn; they support the tuberosities and nothing else. I have a saddle with a short downward horn and the rear is split into two pie wedges which can be swung apart to leave a gap between (don't know the name.)

In any case, if the OP has reason to feel that her coccyx varies downward/outward it will give her a mental image to use to evaluate where to go looking for a saddle.

DX-MAN

Most people default to sit-bone discussions for saddles because: a.)it's Saddle Fit 101; and b.)some may think the OP has adjusted hers poorly, or has a poor saddle to start with, and want to steer her in the right direction. Good intentions. As well, these ARE issues that, taken to excess (which some people do) can result in tailbone issues. I have a niece (26 now), who broke her tailbone in middle school gym class; her frame is such that the tailbone was vulnerable to the type of fall she took. The last few times she rode a bike, she also complained about that type of discomfort; she used it as an excuse to stop riding.

Since I didn't have time when i posted previously, I'll expand on what I WANTED to say. From looking at the bike she linked, I'm wondering also about a too-upright position, which will a.)put most of her weight on the saddle, rather than spreading it out between saddle, pedals, and bar; and b.)make her more susceptible to small angle issues with the saddle re: tailbone. A more upright position needs a degree or few more "back-tilt" to avoid focusing weight on the back 1/3 of the saddle.

BikeFitPro

See if the saddle can be moved back a little. Also if the bars can be rotated forward a little. Ask them if they can make an adjustment to allow you to tilt a little more forward from the hip.
Saddle choice may also be an issue. A shop that has a SwitchIt can allow you to try many different saddles in a very short period of time. Almost everyone is able to self-select a saddle with the SwitchIt by simple going with what feels best. Here is a link to see how the SwitchIt works https://www.youtube.com/watch?v=4w0OU36RfWY
Remember riding in a little bigger gear helps reduce a little weight off your sits bones and distributes it to the feet.
Lastly consider cycling shorts. Cycling shorts are designed to be worn without underwear which can bunch or a seam can cause a discomfort. The design of the padding is made to help aid in comfort.

chaadster

I think this is a very important point. The OP's pelvis probably needs to rotate forward, off the tailbone, and the existing saddle may be fine if she does.

First, make sure there's proper leg extension, then drop the stem (i.e. lower the handlebars) as much as possible. If there's difference to be gained, it could help rotate the pelvis enough to alleviate the pain described.

As earlier suggested, moving the saddle back on the rails could help, especially if the bars are relatively lower to the saddle.

Like others, I'm of the basic opinion that going bolt upright in posture is not the way to gain comfort for riding. It may feel fine and 'natural' at first, but after just short rides, that comfort can go right out the window. While there are saddles and other means of achieving more upright comfort, if cycling for fitness is the goal, the OP would be better served to move towards a more tipped pelvis/angled back position.

Some pictures of the bike and/or pics of the OP on the bike would be much more helpful in troubleshooting the problem no matter what.

LuckySailor

Agree with your first statement! We have these seats on our tandem-Have never liked the Serfas. Picking up Brooks for both of us this week. Too much positive feedback on those seats to ignore anymore.