Just my opinion but unless you are making juice adding sugar to berries does nothing for me.
If the berry isn't sweet it isn't sweet and is made sweet by soil and growing conditions.
As far as freezing either the open layer method and vacuum like Barb said or put in bags.
I always blanch berries an fruit before I freeze them.
Just a quick dip in scalding hot water is enough.
Dip and cool in ice water as fast as you can for the best results.
Regardless nothing is going to take the place of a fresh berry and the best I have seen were what they call flash freezing where they freeze them at extremely low temperatures.
The longer it takes something to freeze the more and larger the ice crystals will be.
I dont have a flash freezer but I do have a freezer that will get well below zero.
Everything I freeze it set out on shelves and allowed to freeze then it is put in bags.
I then use a homemade vacuum contraption to suck the air out.
Works pretty good.
Another option would be to can them with hot water bath in jars for later use.
Worth