Also,if I write 'hand cancel' on the envelope will I need to add more postage?
Unless you mail from the Post Office, writing Hand Cancel on an envelope is of absolutely no use. If you pay at the window, it will cost you an additional 20 cents for them to Hand Cancel it, and I think it still must meet the First Class letter dimensions, thus will need to be under 1/4" thick. If over 1/4" I imagine they would charge you the 'Priority Flat (or Commercial large Envelope) Rate, which is 92 cents for up to one ounce.

It seems that none of the PO clerks are on the same page anymore, and charges are different depending on who you talk to there.

Sad, isn't it?

Sue

Most bubble wrap is 3/16' thick so a double layer would throw it over the 1/4" limit for just one stamp.

Another option, if it is seeds that are quite small, would be to use a double layer of protective foam wrap....see link below. It's expensive, but often when I buy things, there is some foam packaging that I save for miscellaneous uses.

Here is a link that might be useful: 1/16 foam wrap