Going through the diy spouse kitas process is a piece of cake, provided you have all the correct documents. As spicy recommended, you should visit the kantor imigrasi, explain what you want to do and ask them for a list of documents they require. However spicy is mistaken about having to buy forms. All the forms are free. The only fees involved are the published ones for the Kitas itself and MERP (multiple entry/re-entry permit). Putting the docs together is the main work from your perspective, and you have to do this whether you use an agent or not. Also, in Bali these days the home visit only applies to Kitap, not Kitas, probably due to staff constraints. Also, a Bali KTP for the Indonesian spouse is generally only required for Kitap, not Kitas (and even then, I've heard of exceptions).
My wife and I processed my spouse Kitas (as well as subsequent Kitap), without an agent and had no problems whatever. In fact, using an agent would have been a total waste of money and saved us very little time. The people at imigrasi in Renon were polite, professional and efficient. Your situation is a bit different to mine, given you are currently on a retirement kitas, but imigrasi can explain to you and your wife everything you need to do. My advice is to go for it