Q. If for whatever reason I’m not wearing tzitzis, should I wear a tallis at shachris?

(In order to answer and advise you correctly, kindly tell; a) why don’t you wear a talit katan, and b) are you or were you married? Thanks)
Q. I’ve never been married. No real reason why I don’t. Sometimes I do, and sometimes I don’t.
My understanding of the halacha is that it’s only required if I’m wearing a four-cornered garment. If I’m not, then there’s not really a d’oraisa requirement.

A. You are correct that there is no obligation to don a talis and the mitzva is only “kiyumis” that is, you comply with it when you put on the talis and tzitzis attached. However, there are many great benefits in wearing it, as the Torah mentions (Bamidbar 15: 39); “You will see it and remember all the mitzvos.” Tzitzis give us an anchor to the world of spirituality and thus protect us. Our sages say that one who fulfils this mitzva properly merits to have a wife and children. (Midrash Tanchuma, Ki Teitzei). He is also protected from sin,(Menachot 44a) and in that merit he is assured that he will see the face of the Shechina. (ibid. 43b.)
Since the rewards and dividends for one who observes this mitzva are so great, it has become the practice among Torah observing Jewish men to wear constantly a garment (talis katan) which requires tzitzis. If you are unable to do so always, you should put them on as much as you can. Care should be taken, since the Talmud (ibid. 41a) mentions that someone who seeks ways to exempt himself from wearing tzitzis, will be punished in times of (Heaven’s) wrath.
Horav Shlomo Miller’s Shlit’a opinion is that although, never married men in most places don’t wear a talis during davening, there is no prohibition in doing so and in your case it would be the correct thing to do.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit”a