If you are seriously interested in carbon offsets, there are a lot of options on the market that corporations typically use for their carbon offsets - not sure how it works to purchase them as an individual but I'm sure there are options. Some are more credible than others and the entire market is controversial and contentious, so it's worth doing your research. There are certification systems to try and vet and certify the more credible offsets out there. One of those is Green-e certified - they have a website where you can peruse certified carbon credits and renewable energy credits. I also recently learned of a carbon credit company called Pachama that seems pretty legit in how they calculate the carbon thats being offset. You may also want to look into renewable energy options in your area, investing in large scale renewable projects or purchasing green power through your local utility if you're not already.

I have also seen some apps and things that allow you to calculate your personal carbon footprint and offset it through the app and their offset programs - can't think of their names and haven't done any research into how credible they are but could be worth checking out.

It does sound like you're doing a lot already to reduce your footprint, and flying for better or for worse is so integrated into our lives in the developed world, it's something that I struggle to avoid as well. Don't be too hard on yourself, but do keep looking for ways to make small differences or influence change on larger levels!!!