All Covertogs tops have soft cups which are sewn into a separate bodice piece. The top can be modified for use with a prosthesis by either adding a separate mesh pocket or by inserting the prosthesis into the existing bodice cavity and holding it in place by use of velcro or similar.   

If in doubt, The Cancer Society or other organisations might be able to direct you to sewers in your area who have had experience in adding prosthetic pockets. 

You could also try ringing Breast Cancer Foundation on their advice line 0800 2268773 or Natural Wear on 0800 612 612.