Which one or both?
That would depend what type of indoor shooting you're talking about. Is it of people, groups of people, and/or architecture?
My travelling kit consists primarily of the Sigma 8-16 and the DA 15mm. I use the latter when shooting scenes that have the sun in view, and the former for everything else, even for indoor most shooting of architecture.
I was going to get the DA 14mm f/2.8 instead of the DA 15 f/4, but the size difference and the excellent flare resistance of the 15mm won me over.
If the 14mm is too wide, maybe a used FA 24mm or FA 20mm would be good for you. But they're expensive, big, and heavy. Maybe an M 28mm f/2.8 (manual focus), which I used to have could be a solution also.
Some very nice suggestions there, thank you! For this trip I will shoot a small group of people indoors when not outdoors. I have the 8-16mm and didn't think of it at all, especially not after you suggested a small bright prime...