Welcome to the forum! @jeff.mpp
We haven’t used a penis extender, but one technique thing that has worked for us is entering at different angles. My husband sometimes brings me to climax using only the first 1-2 inches of his penis by entering at a sharp angle and grinding just right inside 
Definitely worth trying different positions to find the good spots (not all sweet spots are super deep inside) 
I agree with @Green_Eyed_Girl that a small vibrator is a great first toy to start with (and great for using during penetrative sex)! I really like my desire bullet, we vibe touch and we vibe tango bullet, but they’re definitely on the pricier end… 100% worth it for me as I use them quite a lot, but there are cheaper bullet vibrator options (or if you go with a more expensive toy, you can use the 100 Day Money Back Promise to return it if you guys don’t like it). @Fire_Ice1 recommended trying a butt plug, and I agree - it gives me a fuller feeling during piv sex if I have a plug or finger in the back at the same time 
Hope you guys find some fun things to try together 
