I know its quite difficult to find pajamas out in the stores, I usually get my pajamas from Marks & Spencers as they have a large selection. There are some more options online and there really is something for everyone.
Qoo10 - large variety from adults to babies, I just love the adorable baby pjs.
Libella Bedwear - Conventional, almost traditional cotton PJs for babies and adults.
Roxy - Aussie surfbrand with a few PJ pieces, free shipping for orders more than S$100.
You have a baby - Nursing pajamas for moms.
Mothers Work - limited selection but too adorable baby PJs.
Kooshi - Sells comfy dresses, bikinis and sleepwear.
Tatyana Lingerie - Need I say more, save the embarrassment and shop from the comfort of your home.