Firstly, ask yourself what do you like?  Then quickly follow that question, with another asking about comfort and work requirements?

You need to know what type of safety glasses are required for your work place.  Do they need to be medium impact certified?  Do they need to have a positive seal?  Should they be wrap around/sporty in style? 

What about conductivity? Do need to be conductive (metal) or non-conductive (plastic)?  Do they need to have no metal parts, for example like the Electricians need?

Once you have the answers to the above questions, you are ready to start perusing the prescription safety frame range available.  You can use the filters to narrow this range for you.  For example after you choose prescription safety glasses you can select ladies or men, plastic or metal,  you can also filter the positively sealed frames.

Once you have used the filters to narrow down your selection, then you can start to look for the one that you like the look of.  Once you have narrowed your selection down further then you can look at the measurements (in the additional information) on the frame you like the look of and see how they match the one you are currently wearing.  I recommend trying to match either your sunglasses or your current spectacles as closely as possible.

Please remember when you are ordering that you can not see in the distance with reading glasses.  Therefore would need to remove your safety glasses to walk around.  Which can often be counter productive, to the whole concept of wearing eye protection.