I’m currently a 34 B. I’m planning on doing gummy bear implants to achieve the full C/small D look.

It is important to have a good idea of what size you would like to be after surgery, and bringing photos is a more helpful than 'a full C cup' because we have no standard for how big is a C cup vs. a D cup.  'Gummy bear implants' are are silicone implants that are form-stable, and a 300 cc (or gram) saline vs."ideal" vs. silicone gel implant will all appear about the same size.

At
size 34 B, each 100 cc of implant corresponds to 1 cup size change.  If you want a small increase to size C or D,
you would only need 100 cc to 200 cc. 
Since you have breast fed 4 children you have drooping and need a lift
as well as augmentation.  Unfortunately,
you have not provided photographs but you may benefit from a modified Benelli
technique.  This would lift your breasts
and reshape them creating upper pole fullness. 
For small increases, fat transfers may be superior to implants because
they will not have long term complications and need for revisions.Best Wishes,Gary Horndeski, M.D. 

 Online consultants will not be of much specific help to you.  

 My best advice: further communication with your plastic surgeon.  It is definitely worth spending more time (prior to the date of surgery) with your plastic surgeon to discuss further.  As you know, it will be important for many reasons, that you feel comfortable that you and your plastic surgeon are on the "same page" prior to proceeding.

  Ultimately, careful communication of your goals (in my practice I prefer the use of goal pictures, direct examination/communication in front of a full-length mirror, in bra sizers, and computer imaging) as well as careful measurements (dimensional planning) will be critical.

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. For example, I have found that the use of words such as “natural” or "full C or small D cup” or "proportionate" 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, the use of computer imaging has been very helpful during the communication process, in our practice.

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, after the use of temporary intraoperative sizers.
 
Best wishes for an outcome that you will be very pleased with.