I have a bwd of 13 cm and my breasts are close together. How important is the base width of the breast implant? (photos)

For the purposes of a natural look the diameter of the prosthesis should not exceed the natural diameter of the breast.

Thank you for the question.  Careful measurements of breast dimensions, including breast width diameter is part of the “process” of selecting the appropriate breast implant size/profile for a specific patient. Generally speaking, the best online advice I can give to ladies who are considering  breast augmentation surgery ( regarding breast implant size/profile selection) is:
1. Concentrate on choosing your plastic surgeon carefully.  Concentrate on appropriate training, certification, and the ability of the plastic surgeon to achieve the results you are looking for. Ask to see lots of examples of his/her work.
2. Have a full discussion and communication regarding your desired goals  with your plastic surgeon. This communication will be critical in determining  breast implant size/type/profile will most likely help achieve your goals. 
In my practice, the use of photographs of “goal” pictures (and breasts that are too big or too small) is very helpful. I have found that the use of words such as  “natural” or "C or D cup”  etc means different things to different people and therefore prove unhelpful.
 Also, as you know, cup size varies depending on him who makes the bra; therefore, discussing desired cup  size may also be inaccurate. Again, best not to discuss your goals and/or judge the outcome of the procedure performed based on achieving a specific cup size.
 The use of computer imaging technology may also be very helpful during this communication process.
3.  Once you feel you have communicated your goals clearly,  allow your plastic surgeon to use his/her years of experience/judgment to choose the breast implant size/profile that will best meet your goals.  Again, in my practice, this decision is usually made during surgery. I generally select appropriate breast implant size/profile after the use of temporary intraoperative sizers and viewing the patient's chest in the upright and supine positions.
I hope this (and the attached link) helps.

There are several important points to be made here

Your plastic surgeon should be the one guiding the decision making process when selecting implants.  The plastic surgeon should be placing an implant that fits each patient's breast well.  The base width is important when considering the implant because it serves as the base of the breast.
Here are some important points to keep in mind when selecting a surgeon for your breast augmentation

1. Make sure you have a good conversation about your goals with the plastic surgeon.  The surgeon and you can then come up with a good size and shape of implants to fit your breast.
2. Make sure the plastic surgeon is BOARD CERTIFIED by the American Board of Plastic Surgery. This is very important and you can search to confirm this.
3. Make sure you see the plastic surgeons before and after results.  Make sure his photos are in line of what you expect out  of the surgery.
4. Make sure you feel comfortable in the surgeons office with the staff.  At our office we treat our patients like family and are with them EVERY STEP OF THE WAY.