Giving frozen milk is totally fine! You can even give ur baby frozen BM that is up to 1 year ago but optimally, use within 6 months. If baby is fine with ur frozen BM, don't really need to give fresh milk. But u may also alternate fresh and frozen for different feeds just so tt baby cld get the best nutrients and antibodies frm ur fresh BM at certain times of the day.
There are other kinds of reusable milk storage bags but it's kinda hard to find in SG. Can try searching online. Or use Avent milk storage cups, though tt will take up more space in the freezer. For me, sometimes I use the milk cups if I just want to chill in the fridge but gotta use it within 3-4 days.
Or u can use food cube trays. I used this in the first month when I was battling with low supply. I cld barely fill even half of the storage bag. So I poured my milk into 2oz food cube trays. It was rather convenient too as my baby was drinking abt 120ml so I just had to take out 2 cubes to warm it up.
bunsoh