I installed all of the baseboards today. I used basswood strips that I bought at my local craft store. They are in the wood crafts section. I bought the narrowest ones I could find to keep to the scale of the dollhouse.
I also trimmed the bay window openings. This dollhouse brings trim for the openings but it is very narrow and so I preferred to make my own.
You can already see the difference that interior trim makes so even if you have to buy the simple trim that I use, rather than expensive real miniature moulding, then it's well worth it. You wouldn't want to skip this step.