Effectiveness of fat transfer for small breasts? (Photo)

35 year old trans woman 4 years on estrogen with very minimal breast development. I'm underweight (18.5 bmi) and lacking in visible body fat in many areas, mainly of concern is on my chest where my sternum is clearly visible. I only want to get to about a B cup and would prefer to avoid the complications from implants if it's possible to get noticeable results with fat transfer alone. Would it be too difficult to even gather enough fat for noticeable results?