Clothing isn't really a big deal. I bike everyday in heavy cotton clothing and jeans.
To the Thread Question:
I find swimming to be more boring and you won't burn as much weight. I lost 100+ lbs biking and eating a little less. If you're loosing weight only during summer, that sounds like you either aren't eating correctly in the colder seasons or aren't as active.
The best way to loose weight is to change your eating habits, fast food and soda, then workout. Don't think that if you walked to the store, that's a workout. You need to forcefully workout and call that a workout everyday. After you loose weight a bit and you won't loose another pound, then you change your diet drastically and go low carb and low fat.
Just my two cents.
If you want to buy cycling clothing, I would say to go to a local sports shop to try on the clothing.
Or you can find alternatives to this.
I like a a thin, long shirt that's brightly colored, nice fitting and not baggy shorts, long socks that you can sacrifice to only biking because of the chain oil rub. it depends on what pedals you're using for a shoe type.
If you're using clipless, that's a give in.
If you're using toe clips and straps, you can use anything that will fit into them. I would go with a stiffer walking shoe
If your platform, stiffer with less give on the sides is nice.
Remember, loose the weight, and keep it off. Good luck!