[Drew]

Hi, Perky,
I'd suggest a few tweaks to a good chest exercise regimen.
First, you'll want to do Decline bench press. It will build the lower section of the Pectorals, meaning: More growth underneath, simulating underboob.
Second, for that part, do it as bodybuilding: Chase the pump. I've got programs where it's 3 sets, using dumbbells, if you were to do 10, 15, 20 pounds, in a pyramid of 12 / 10 / 6-8, you'd get the results - take 30 seconds rest between sets, don't move on to a different body part. Squeeze hard as the muscles contract, hold for a second with the squeeze at top, then let them down under tension.
Flyes would also help, but I wouldn't worry about the protocol there - the tightness won't align with bigger boobs. If you go digging, though, you might find something to push the boobs to the mid-line of the chest (as we tend to have an East-West nipple split, one points to the East / Right, one to the West / Left. Want to make them point straight ahead.)

I's also do a pre-fatigue approach, lighter weights, more reps, do high volume pullovers, something like a weight of (80% of 1RM) type of thing, nothing fancy. One set of 10, probably - per article at T-Nation (bodybuilding site), the extra sets of a standard (weight) * 3 sets X 10 reps/set doesn't do much. But doing a lighter weight for reps would work well, say, if you could really lift 100#, do 20# for 100 reps. Or, the 80% 1RM would work, for a set of 10. Whatever suits. Then the Flyes or a crossover cable, to get the muscles additionally fatigued, "Normal" weight, 10 reps, again. Stretch a little while resting, then do the HARD sets of the dumbbells in decline bench.

Nod to Renee Reyes (https://www.reneereyes.com/Crossdress%20Survival%20Guide/Crossdresser%20Transformation/Crossdresser%20Exercise%20Tips/index.html and https://www.reneereyes.com/Crossdress%20Survival%20Guide/Crossdresser%20Transformation/Transgender%20Arm%20Reduction/index.html)

This should get you the Pump feel you want, AND avoid too much arm development.

Note, you don't want to do actual ARM exercises, if you want to feminize. If you want to retain male strength, I don't know how to guide you - strength usually relates to size, you could work with plyometrics or body weight exercises with volume, but you'll retain size and tone, so you'll have to feel your way forward, trial and error.

Best of luck!
-Dianna

Very good advice, stamina training as opposed to body building is the way to go. Training the chest, well you need to use your arms to do that and there is the danger that your arms will develop that's just how it is so there is a fine line between keep my skinny feminine arms or sacrifice that at improving my chest.
Please correct me Dianna if I'm writing crap now am not an expert but I do nothing at fear of developing masculine biceps again. But exercise can be important I do exercise to tone body parts, I do crunches to tone my belly....well that didn't work too well to be honest I got a six pack from overdoing it which just looked stupid on me. I do still use light dumbell's to tone my triceps as I'm afraid of getting those loose hangy ones that even a woman gets with age.
Exercise to tone body, to even tone a body to be more feminine is an absolute plus.