I think you will need a lift if you downsize
Your implants are quite large for your shape. You already have once known as bottoming out, where the distance from the nipple to the inframammary fold has stretched out. If you go with a smaller implant, in order to achieve the best shaped breast, you will need a lift either at the same time or as a secondary procedure. I do a lot of revision breast augmentations/lifts
Downsizing implants may require a lift but not always
Downsizing your implants will help prevent problems down the road, since they are already stretching out the lower half of the breast and bottoming out. There are various ways to reduce the pocket for the new implants. A lift is considered for two reasons: One is the raise the nipple-areola (which does not appear to be necessary in your case) and the other is to reduce the skin envelope to match the new size of the breasts with smaller implants. That will depend on the elasticity of your skin and the size of the implants so there is no way to answer definitively online.
Downsizing breast implants, without a breast lift?
Thank you for the question and pictures. Yes, it is possible to downsize breast implants, without undergoing breast lifting, in your case. This procedure will likely involve capsulorrhaphy surgery, which refers to decreasing the size of the breast implant capsules ( which are simply the layer of scar tissue around the breast implants). Given your youth ( better skin elasticity), careful selection of breast implant size/profile, and careful execution of the procedure, it is likely that you will achieve a very nice outcome.
I would suggest that you select your plastic surgeon carefully. Ask to see lots of examples of his/her work helping patients achieve the types of outcomes you are looking for with revisionary breast surgery. Then, make sure that you communicate your goals carefully as well. In my practice I find the use of goal pictures very helpful during this communication process. Achieving realistic expectation will also be important when it comes to patient satisfaction with the outcome of revisionary surgery in general. I hope this, and the attached link, demonstrating similar procedures, helps. Best wishes.
Yes down size without lift but the pocket must be controlled
I completely agree that you would benefit from downsizing of your implants. You have bottoming out and the Infra mammary folds (IMF) are asymmetric. The surgeon must be very meticulous in elevating and securing the IMF and the lateral border of the pocket. It looks like you need to elevate the IMF by 3-4cm. The stitching involved in the new IMF must be immaculate so it will not have puckering or distortion and will have longevity. The use of Acellular Dermal Matrix is not a guarantee and is not needed in my experience. It's about the placement of stitches, the number of stitches, and the time spent doing it.
Oh, by the way, you don't need a lift
Good luck and take care.