Yes you can get WC on yourself speak to your insurance carrier for your General Liability. You will pay a rate based on a min. salary for yourself. If you should make more that that min. salary you will pay the difference. You will get an annual WC audit from your insurance carrier.
For mowing you should be more on the 8-9% range maybe even lower. You can also go through a payroll company such as Paychex. In this scenario you are only paying based on your weekly or biweekly payroll. Pay as you go rather than a 50% premium payment followed by monthly installments. I guess you need to ask yourself what happens when YOU get hurt. Do you have the money saved to live and pay your medical bills?
That one or two guys you have working every now and then can cost you big if they get hurt, especially operating as a DBA. I know most guys will say its a friend or a family member so I'm not worried about them coming after me. Consider the worst case scenario and someone chops of their hand. Do you think they will just say don't worry about it? You will be liable for all medical expenses and lost wages plus the settlement for losing a hand. Then your state will come after you with fines for everyday they worked for you without WC Ins.
You should consider incorporating or becoming an LLC. Most attorneys will give you a free consultation on what would work the best for you.
When you think of the possibility of the above happening it's really not expensive it's just a cost of doing business.