When that happened to me as a freelancer, I subcontracted to other freelancers. Gives you much more flexibility and less overhead. I found them through the same

When that happened to me as a freelancer, I subcontracted to other freelancers. Gives you much more flexibility and less overhead. I found them through the same freelancer sites I used to seek work through - though I understand the race to the bottom on those has accelerated. In terms of billing, just look for someone who charges a lower rate than you do - whether it's because they're less skilled (in which case, account for the extra time they'll need to get things right) or they're in a location with lower costs but less opportunity to network with high-paying clients. I also recommend raising your own rates. If you have too much work, that means you're in enough demand that you can afford to let some contracts go, especially if it means you'll be paid more for the remaining ones. It also gives you more room to work with in hiring subcontractors. You can appease your existing clients a bit by announcing a significantly higher rate for new clients and then reassuring the old ones that they're grandfathered in for the next N months at current rates and then you're only subjecting them to half the rate raise that applies to new clients, or something to that effect.