Informal:
* Cariad mawr: This literally translates to "big love," and it's a common way to express lots of love in a casual setting.
* Lliw o gariad: This translates to "a colour of love," and it's a more poetic and playful way to say "lots of love."
Formal:
* Cariad llawn: This translates to "full love," and it's a more formal and heartfelt way to express lots of love.
You could also use a combination of these phrases, like "Lliw o gariad mawr" (a colour of big love).
Ultimately, the best way to say "lots of love" in Welsh is the way that feels most natural and heartfelt to you.