Its such a challenge and a worry isn't it? Especially hard in those first few weeks when you are recovering from the birth and sleep deprived. It does get better though.
We have 18mths between Dominic and Isobelle and its been hard, hard, hard! But as Dominic gets closer to 2 things have changed and it is getting easier.
I found having lots of activities out for Dom to bounce (literally!) between really helps. He has a library corner and toy corner in the lounge where I can keep any eye of him when feeding Issy and I set up drawing at the table. I have a pile of books beside me when feeding as well, as he tends to want to be close when Im holding Isobelle.
I give him as much attention as I can when she is sleeping so he doesn't feel abandoned by me, or rather to apease my own guilt and worry about him feeling like that.
Often I will give him morning or afternoon tea (depending on time of day) when I feed her too.
I always make sure there is a drink of water where he can see and reach it in case I have my hands full.
I also try and involve him in caring for her, in a limited way of course as he is so little himself. He comes in with me to get her up and plays with her on the playgym. Watches nappy changes and baths. We sit and talk about her, point out her toes, fingers, nose etc. Its a nice way to all spend time together, a respite from that constant guilt that one baby is missing out.
If you can swing it the having a nap at the same time thing is great. When they are really little it doesn't always work out but as your youngest settles into her routine more it will happen more often.
When going out its all about planning and timing.Its hard getting out of the house but going to playcentre has been great for us too. There are lots of supportive mums, other children for Dom to play with and a whole lots of new activities. He loves it.
I definately agree with busymum that feeding while discipling is the hardest but if I need to I just put Isobelle down for a few minutes and deal with it.
Hang on it there in, it will get better even in just a few months (as everyone adjusts to the new family member and new routines) you'll probably notice a difference.