I am a huge, huge fan of Westones so maybe I can actually contribute something here. At some point, I have owned the UM1, UM1 Corsica Edition (same thing as the regular UM1), W20, UM3x, and W40. There are some pretty massive sound differences among them so you should know which ones you may like before purchasing them. I keep coming back to them because of Westone's outstanding customer service and the comfort level of the various models. Westone's in-service warranty service is fantastic, and they will repair anything for a fairly reasonable cost out of warranty. The one knock that I have found on their earphones is their durability. One earphone usually goes out on them after a year or two. The W models are made in China and the UM ones are made in the U.S. so that may have something to do with it. If you can take care of them, they are the best earphones for the money. If you take them to the gym, I would highly recommend that you purchase the Westone "Monitor Saver" for $10, which is a plastic container that has a pod of silica gel on the bottom and does a good job of taking care of sweat and moisture.
UM1: I used these as my knockaround and gym earphones for several years. Very accurate with a great midrange, but no low bass of which to speak. It's not a fit issue; the earphones do not really extend below 40 hz, and I suspect they start rolling off earlier than that. As a result, they can be thin and sound a bit harsh. When I bought my first pair almost 10 years ago, they were the best value in the $100 range; now, I believe that they may have been surpassed by some other models by different manufacturers. Still, if you are a midrange junkie, you can't go wrong.
W20: These sounded great, except for one major problem: They kept breaking with one channel going out each time. When they worked, the fundamental sound signature was like the UM1, but with (very tightly controlled) bass this time and a smoother overall sound signature. A great buy for the price and one that I would wholeheartedly recommend except for the durability issues. After sending them back for repairs twice and them breaking twice, Westone generously upgraded me to the...
UM3x: I love, love, love these earphones. Huge, warm, all-enveloping bass with a butter-smooth midrange. The treble, while present, is recessed a bit due to the mammoth gobs of low-frequency energy. The thing about the bass on these earphones is that it is not really accentuated in the sound signature. It is just present, like a boulder or an elephant. I listen to a lot of hip-hop and jazz, and these were great for those types of music because the bass is powerful, but not punching you in the face like a pair of Beats. The soundstage is very tightly defined with clear limits as to width and height with great imaging so you can clearly define each instrument and where it is placed. These earphones are just a lot of fun and work well with all types of music. After six years of dutiful service, they gave up the ghost when I was in the airport and was about to go on an intercontinental flight, so I ran to the shop in the airport and picked up a set of...
W40: These are truly reference-caliber earphones and are the best ones that I own. They have everything: refined, smooth presentation, incredibly well-integrated drivers, seemingly limitless bass and treble extension, and pinpoint soundstaging. The airport store let me compare these versus the Shure 535 SE and I preferred the Westones because of their superior driver integration. I read some reviews that said that this model does not have a very engaging presentation, but I want the music to be engaging and the headphone to reflect exactly what is playing. For that reason, the W40 is the best in my view. Yes, they cost a small fortune ($500), but I fully expect them to last the rest of my life. The other thing that is interesting about this model are the detachable cords so if an earpiece goes out (something that has happened with almost every other Westone that I have owned), I can try to replace the cable instead of send the earphones back.
My recommendation would be to get the W20. They are a clear improvement over the UM10 (and, I suspect the W10), and offer much of the benefit of the higher-end Westone models for a fraction of the cost. Westones are the most comfortable earphones that I have ever had and their profile would be what you like. I would also recommend ordering from a retailer like Earphone Solutions that offers an extra year of warranty service for a two-year warranty if you order from them. That way, you will have the comfort that you need if anything goes wrong. Also see if the W20 has detachable cables like the W40; that is another feature that can come in handy.