Sorry to hear that Ibu Oka didn’t live up to your expectations. Its standards are not very consistent.
I usually trawl Indonesian language food sites as I’m hoping that local food-bloggers might give some good tips targetted at Indonesian domestic tourists rather than us foreigners.
Two oft-mentioned babi guling spots are Pak Malen (in Seminyak) and Men Agus (Mengwi). I’d not been to either so cannot personally vouch for them:
Three years later and I’m also in Ubud finding it rather hard to find anything other than mediocre food at least in the cheap eats category. We had a good meal at Hujan Locale, but our budget for this trip means we’re trying to stick to warungs.
Tried going to Ibu Oka today as I felt it was obligatory but I dithered a day too long and it’s closed for Galungan tomorrow, along with another babi guling spot I tried to visit. Oh well, reviews seem extremely mixed these days!