Left sided mastectomy. Bras?

A mastectomy bra is the easiest option - both cups have pockets to hold a pad (in the early days) and then a prosthesis. To be honest, I wore my normal bras for ages with a soft pad but I don't recommend it, the pad had an annoying habit of moving! My oncology nurse provided me with a soft cotton form which I could fill with padding to the right size. Others have used knitted forms (check out Knitted Knockers!). I recommend getting fitted properly for a prosthesis if you decide to use one - I had a specialist who came to my home to do that, but my local Myers (Melbourne) has a good section for mastectomy bras, prostheses and swimwear.  A Google search on mastectomy bras should throw up local stockists.

Drains vary a lot - mine were done in four days but they may take a couple of weeks. It's best to let any fluid run its course, annoying as drains may be.  

Waiting to see how you go can be a good plan, even if you do decide on reconstruction later - it gives you time to adjust and recover. Just be aware that a soft pad is harder to adjust to than a prosthesis, it doesn't have the right weight and often doesn't feel like a part of your body. But it is the best option until your surgery is well healed. Best wishes.