Advice for Breast Augmentation Redo After Pregnancy?

Puitting a larger implant will make it bigger and tighter in the short term but set you up for sagging in the long term.
It sounds as if you are recieiving conflicting advice and that makes it difficult to make a decision.
From your picture, it appears that you have relatively litttle sagging according to our classifications. I would be reluctant to adivse you to do anything at this time if you are looking to have them high and tight. This is especially true because you state that your first augmentation did not achieve this goal
If that is your goal, one option is to consider a reduction and a lift to elevate the existing breast tissue and then place a similar sized implant without necessarily increasing the size of your breasts. Be prepared for the scars.

The choice for breast lift or mastopexy is dependent on the degree of skin laxity and the position of the nipple. Larger implants will temporarily improve the position of the implant if done appropriately, but this will inevitably result in further droopiness of the breast and nipple. I would suggest a breast lift with or without exchange of your implants.