Have you seen the Hanshew forward extension? Works really well and is only about a half ounce. This link looks weird but it is the actual webstore for Hanshew:
https://1ds4cg-mw.myshopify.com/
If you find it suspect (wouldn't blame you), Google Hanshew forward extension.
I've got one and it works pretty well. I put it on my break stick and can hit most balls on the table. It's pretty nice because it's light, you use your normal stroke geometry and it's on/off about as fast as a quick release rear extension.
For a rear extension, I've got a local cuemaker friend making a rear extension out of a CF tube with the goal of being as light as possible. I told him I want the goal to be sub 2 ounces for an 8 inch extension. I'd like it to be 1.5 ounces or less but we will see what happens. I bought enough materials for him to try a couple different configurations.