There is an easy solution. My neighbor has a beautiful house with banisters looking down to the front door at the foyer. She has 3 little grandkids who visit often. Because she didn't want to have to worry about the stairs or the banisters, she had a company install a custom gate at the top of the stairs, at the bottom of the stairs, and plexiglass where the spindles are. You barely notice the plexiglass - it is really well done!
The older child doesn't need this anymore, but there's another grandchild on the way, so she will leave these up for several more years. Having it done custom will ensure that it fits perfectly, won't pinch little fingers, and will look good. I highly recommend that.
If you look at the cost versus a few ER visits, you will know that this really is affordable.
For the rest of a house, just babyproof as much as you can and do your best not to worry too much!
Dawn