Is a 450cc under the muscle, high profile, silcone right for me?

Thank you for the question. However, despite good intentions, online consultants will not be able to provide you with  meaningful specific advice.  Ultimately, in person consultation with well experienced board-certified plastic surgeons will be necessary. Careful measurements, dimensional planning, and careful communication will be key.
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're 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 which operation and/or 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 who makes the bra; therefore, discussing desired cup  size may also be inaccurate.  The use of computer imaging may be very helpful during this communication phase.
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 hope this, and the attached link, helps.

Unfortunately,
you have not told us your bra size just your cup size. If you are 32 or 34 each 100 cc’s of implant
corresponds to 1 cup size change. If you
are 36 or 38 each 200 cc’s of implant corresponds to 1 cup size change. From this, you can compute the volume
required to achieve your desired goal.
450 cc implants are large, will extrude inferiorly and laterally
requiring revision. Since you have
breast fed, you may benefit from a simultaneous lift. I recommend a new technique called Breast
Augmentation with Mini Ultimate Breast LiftTM. Using only a circumareola incision it is
possible to reshape your breast tissue creating upper pole fullness, elevate
them higher on the chest wall and more medial to increase your cleavage. Through the same incision, implants can be
placed. Aligning the areola, breast
tissue and implant over the bony prominence of the chest wall maximizes
anterior projection with a minimal size implant. Small round textured silicone gel implants
placed retro-pectoral look and feel more natural, are more stable, less likely
to ripple or have complications needing revision. Implant profile is irrelevant in the
retro-pectoral position since the muscle compresses it. 22% of women who undergo breast augmentation
alone require revision within 2 years because they are dissatisfied with the
result. Frequent causes of
dissatisfaction are over implantation and not performing a simultaneous lift
when needed. Best Wishes,Gary Horndeski, M.D.

Thank you for your question.  Your best option is to follow the advice of your plastic surgeon after an in person consultation and breast implant sizing system exam.You may also try the Rice test at home.  In addition you may read about the Mentor Breast Implant Sizing System in the link below: