We have started BLS but he's not really ingesting much yet. I do think he'd probably get more in if we spoon fed so I guess this is option 1: do you think it would be ok to give him a little spoon-fed meal of something easy to digest to fill him up so he lasts

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This is what I would try first. You may find you not being around changes his pattern anyway and he will feed more often when you are about and last longer when you are not.

Have you tried being a away 5 hours to see what he is like at all? Get in a couple of feeds closer together and then go out?

DS would never take bottle and I also hated expressing, and I was lucky in that if I was around he would want it but if not was happy enough and just ate/played with food and had water and then made up for it after.