New items and no clue how to add proper shipping

I am expanding my store, and have recently opened up a new line of products that does not fit the same shipping schema that I have been using.
Previously, I was selling only packets of seeds, so the shipping costs were very simple to do, and flat shipping covered all of my needs.
However, now, I am and carrying items that I have not yet added as live to the site. These are items that have differing shipping requirements. Be it weight, packing, or handling.
Rather than make a flat rate shipping for all items, how would I make it so that I can add the individual shipping charges to the item and not change any of the other items I am selling?
I am carrying hundreds, soon to be thousands of different seed varieties, and this is the basis of my business, but the new items I am adding will also be something that I will be carrying/offering permanently as well, and really have no idea how to add the shipping for them properly.
Kirby
https://www.downrightnatural.com

You could create an attribute named "Additional Shipping Charge" and assign that attribute to your non-seed products with an additional price to be added.

If you were to enter the shipping charge in the Product weight field, would you be charging just that shipping cost for quantity 1, 2, 3 or that shipping cost multiplied by the quantity?

More or less the idea is add up the total weight of these products which is their shipping cost and add it to the current Flat Rate that you charge for the seeds ...

Would I just add this as a price offset or some other way?

If you could tell me what kind of shipping cost you are looking to do for these products.

Example: if you were to enter 1.25 into the Product Weight, to indicate a $1.25 shipping cost would you want to charge:
A) 1.25 for any quantity
B) 1.25 x quantity ordered

Currently, I am charging a flat rate of $3.99 for all the items that are in my store, no exceptions for the current inventory.
I am expanding that inventory with items that are being drop shipped as well as added to stock I have on hand.
There is a charge that I am being assessed by the drop shipper, this is a flat rate of $17.99.
How would I add that additional cost to the items that need to have the additional charge without affecting the current flat rate system that is in place.
I would also like to not have to roll it into the price of the item, this will loose me sales when people comparison shop the item.

If I order:
1 Seed $3.99
1 Other Product $17.99
Total Shipping $21.98

If I order:
5 Seed $3.99
1 Other Product $17.99
Total Shipping $21.98

If I order:
1 Seed $3.99
3 Other Product $17.99
Total Shipping $21.98

If I order:
3 Seed $3.99
3 Other Product $17.99
Total Shipping $21.98

Correct?

Mostly correct. The seed is flat $3.99 for any quantity. The other items are all individual shipping. (Each item must be packaged and shipped individually to ensure they are not damaged, and cannot be packaged in the same container.
So:

YES
1 Seed $3.99
1 Other Product $17.99
Total Shipping $21.98

YES
If I order:
5 Seed $3.99
1 Other Product $17.99
Total Shipping $21.98

NO
If I order:
1 Seed $3.99 YES
3 Other Product $17.99 NO SHOULD BE: 3 x $17.99=$53.97
Total Shipping $21.98 $57.96

NO
If I order:
3 Seed $3.99 YES
3 Other Product $17.99 NO SHOULD BE: 3 x $17.99=$53.97
Total Shipping $21.98 $57.96

I really appreciate the help with this. I am very lost and you are taking the time to help, and that is amazing!
Thank you,
Kirby

If you were to enter on these Other Products into the Product Weight of 17.99 ... would the total weight of the be the correct shipping cost when you order:
1 Other Product

-Or-

3 Other Products

-Or-

1 Other Product quantity 3

-Or-

3 Other Products quantity 3 of each