I been wanted to try out different kinds of underwear to see which one I like, but I don't want my mom to think I'm obsessed with it.
Also is it bad to have condoms in your room, even if you don't plan on having sex at all?
Clothing always eventually wears out, so buy a different style and see how you like them. If you don't, you can wash them well and give them to some charity. But just buy one style at a time to give them a try. When you find the one you like, just replace your old ones with the new style as they wear out.
I'm curious would you buy food that you have no intentions of eating? Or purchase cigarettes that you have no intentions of smoking? Buying something means you have thoughts of using it. Christians should not be engaging in sex outside of marriage, which is what condoms in a single man's room indicates. Anyone finding them would have legitimate questions as to what your purpose is for having them there. You have to consider not only your intentions, but the impression you leave with others. "Providing honorable things, not only in the sight of the Lord, but also in the sight of men" (II Corinthians 8:21). My only guess is that you are wanting to leave a false impression for someone else, and that would be dishonest.
What are some ways of buying them? I feel embarassed buying underwear. What about masturbation? I want a straight forward answer; is it ok or not? If so, I prefer doing it in the shower because it washes away easily, but the only shower we have is a room with shower heads. I'm out in the open. And I want to go to a Chinese bathhouse is that OK becasue I will be exposed.
You are being inconsistent. You talk about being embarrassed to buy underwear at a department store and being afraid that your mother might find out you are trying different styles. You talk about being embarrassed that your roommate might see you with a morning erection. But then you talk of wanting to go to a Chinese bathhouse where people bathe in sight of each other and where prostitution is prevalent.
A Christian has no business supporting, through their patronage, businesses that encourage immoral behavior. "But fornication and all uncleanness or covetousness, let it not even be named among you, as is fitting for saints; neither filthiness, nor foolish talking, nor coarse jesting, which are not fitting, but rather giving of thanks. For this you know, that no fornicator, unclean person, nor covetous man, who is an idolater, has any inheritance in the kingdom of Christ and God" (Ephesians 5:3-5).
Being naked is called shameful by God. "Behold, I am coming as a thief. Blessed is he who watches, and keeps his garments, lest he walk naked and they see his shame" (Revelation 16:15). In the Old Testament God said He would expose Babylon's sins to their shame and He draws the same parallel. "Your nakedness shall be uncovered, yes, your shame will be seen" (Isaiah 47:3). It was such an embarrassment that God used it to illustrate the exposure of sin in a person's life. Micah too talked about the shame of nudity. "Therefore I will wail and howl, I will go stripped and naked; I will make a wailing like the jackals and a mourning like the ostriches, ... Pass by in naked shame, you inhabitant of Shaphir; the inhabitant of Zaanan does not go out. Beth Ezel mourns; its place to stand is taken away from you" (Micah 1:8, 11).
There are going to be times when you cannot avoid being seen naked by others. You and your roommate are going to see each other at times while you are changing, though there are ways to minimize this. You will be seen and see others while you are showering. But even in these situations, there are some attempts at privacy. It is not that just anyone can walk in on you. And even here you should make attempts to limit your exposure.
In regards to masturbation, see:
Masturbation, by itself is neither right nor wrong. It is a bodily function. But when sinful thoughts are used to trigger arousal in order to masturbate, then it is wrong because the lustful thoughts are wrong. Since your showers are open, you'll have to find another way to ejaculate that remains private.