Try using the
Alchemy Calculator on the wiki, to see what easy combos will work for you.
Flax seeds are a v. common, light weight, and pretty easy to get though, and will mix well with your Strawbs and Peonys. Travelling to Skingrad and on to Anvil, you tend to find alot of flax.
Basically you prob want Flax and Nightshade, and then mix them with the Strawbs and Peony that you already have. You can also use Venison instead of Flax or Nightshade, but just make sure that you use Flax or Nightshade for the first potion, and then w/o going out of the Alch mixing page, switch to Venison, and your resultant potions should still keep their low weight. Otherwise the Venison potions will weigh you down pretty quick.
But I just love Alch anyhow, there are some fantastic pots/poisons that you can make, and sounds like you've already got pretty good stores of ingredients. Good luck!