To answer this question, you need to decide on the following:
Format of the class: one-on-one with an instructor, group class, or online class or https://www.julianalucky.com/post/all-about-pikler-triangles-your-ultimate-guide;
Composition of the group: male/female or mixed;
Purpose of the practice: physical development, mental perfection;
Yoga style: ashtanga vinyasa yoga, yoga 23, Iyengar yoga, kundalini yoga, hatha yoga, yoga in hammock, yoga nidra, etc.
In other words, you need to be aware of how dynamic the practice will be, whether anyone will see you, and whether the style you have chosen includes traditional clothing (for example, Kundalini Yoga practitioners wear a special garment, usually white, that includes a turban on their head in addition to loose pants and a shirt). If it is a dynamic practice, one should not wear too many clothes, and they should not hinder the movements. For some people it is important to wear clothes with moisture wicking properties, but this is only possible with synthetic clothing, and this is something everyone must decide for themselves. If you practice more relaxed types of yoga, it makes sense to choose as natural fabrics as possible. If you practice with a trainer and it is important for him to see the relief of your body, a tighter fitting garment is suitable.
Yoga clothes should allow you to go deep into any asana, be it a split, a bend or a bridge. Care should be taken to ensure that the upper part of the uniform does not bulge when you bend over, and the lower part does not hinder movement when you spread your legs. If you prefer a long T-shirt, it should be long enough to tuck into your pants so that it does not become loose when bending over, bridging or standing on your head.
In yoga nidra, you lie flat on your back in shavasana for a long time, so you should choose clothes that prevent you from freezing and make it comfortable to lie flat for a long time, i.e. no buttons, ribbons, zippers, knots, etc. on the back of your body.
Why is it useful to pay attention to the composition of the group? Because when you practice yoga not only in form but also in essence, you should not miss the energetic moments associated with focusing on yourself. So if you are a girl practicing in a mixed group, it is better to wear a more modest uniform so as not to distract young men and men from the practice. This problem is not so acute in mature yoga groups, where everyone is focused on working with themselves and the inner world during practice. However, the more modest the girl is on the mat, the better for her practice.
If the goal of the exercise is to feel the energy flows as much as possible, choose loose-fitting cotton or linen clothing. If the exercise is not intended for vigorous movements, it is better to wear loose-fitting clothes made of natural materials: it allows the body to breathe and nothing hinders the free flow of energy.
Have fun practicing!