Going with bigger implants won't lift the breasts
You actually don't need to go bigger at all unless you want to be bigger. If your nipples are heading south, going with bigger implants won't restore them northward, you need a lift to do that.
Bigger implants no good for 38DD.
1) Don't do it! You will regret it. Trying to correct sagging breasts with large breast implants is one of the most common mistakes that I see in Manhattan. You will not look natural and you will still have sagging. Very large breast implants age very badly.
2) It sounds like you need somewhat smaller implants and a good breast lift with a lollipop scar. Women accept breast lift scars very well if they love the shape of their new breasts.
The WOW factor in redoing your Breast Implants
If you need your breast implants redone, it may be time to take a close look in the mirror and see if what you really need is a lift. If the implants are soft, they may already be large enough.
The second most important question now that you've lived with implants is ... do you really need them to be any bigger? A proper lift can be done irrespective of their size. Many think they need them bigger but are perplexed at why they are dropping so much.
Perhaps the descent of the breasts is related to the sheer weight of the implant. People's breast tissues drop even if they don't hold up an implant, so consider decreasing in size. The more you decrease in size the more your lift will be necessary.
Lastly, keep in mind that expecations may be the most important element in this particular operation. Spend some time with your plastic surgeon and review EXACTLY what to expect because this time it is very different than when you had them done for the very first time.
Bigger breast implant exchange may not work well
This is a common thought process that may not work well for many patients. You are already a DD cup and therefore probably have large breast implants in place. The bigger the implants, the less of a difference you will see with going larger. This is because if you add 100 ccs to a 100cc implant you double the size but if you add 100 cc to an 800 cc implant you may not see that much of a difference.
In addition the rate of drooping increases with increasing volume of implant. You will almost certainly be heading for a breast lift. You could have it now or you could have it later but it is quite likely that you will need one.
Larger implants to avoid breast lift
The answer is yes--larger implants will allow your nipples to be higher on the breast mount thus avoiding a breast lift. However, you would probably require a sizeable increase which will only accelerate your breast ptosis (sagging). The better solution is to have a breast lift. It is true, that a breast lift will require more scars on the breast, but you will be able to keep the same size implants. This will also allow your breasts to remain "perkier" for much longer before requiring reoperation compared to just placing larger implants. In order to get a more personalized answer to your question, a physical exam with a board-certified plastic surgeon is really what you need. Good luck!
Bigger breast implants not the answer for sagging breasts
As you sag, you will find that a Mastopexy or breast lift, is probably the surgery you need. The larger the implants, the faster they sag. Remember, gravity always wins.
Bigger implants not the best choice for a lift
The temptation to solve the sagging breast problem with bigger implants is appealing because no one wants the scars from a lift if possible. The trade-off, however, is that bigger implants will lead to even more sagging over time. If you are already a DD then going bigger just doesn't sound like a good choice. Though every situation is different, most of the time in a situation like yours going smaller and doing a lift makes the most sense. You could of course just do the lift and leave the implants alone if you like the size you are now. Scars from a breast lift typically fade very nicely and patients are happy with the improved shape.
Breast implant size for replacement
Unfortunately, your questions are very generalized and no photos are posted. My guess is a slightly larger implant and some type of breast lifting is in order. Best of Luck.
Implant removal and replacement or lift with sagging large breasts
It is more likely that you would benefit from a breast lift (mastopexy) procedure in contrast to implant removal and replacement. In this instance, you could also decrease the size of your implant and breast tissue if you desire to minimize the risk for long term recurrent sagging.
Breast lift may be necessary
What size you choose is really up to you. You don't have to go bigger or smaller, however you may want to consider getting a different profile to help you make your breasts appear perkier. If that doesn't help, a breast lift may be necessary to address sagging more effectively.