Apologies in advance for a long, waffly post. But I'm very pregnant and obviously quite tired :)
You say you want to do it yourself. I managed it (sometimes by the skin of my teeth) so I can only tell you what I did. I'm writing this as much to remind myself. And of course I have my 2 DDs to look at and think - well they seem to be turning out OK (they are now 5 and 3.5).
Get up in the morning and get dressed, even if you don't shower. I just feel that tiny bit more in control if I'm not in my pyjamas. If possible get DH to do breakfast for DS, while you sort out baby and EAT YOUR BREAKFAST (I am really bad at remembering to eat!).
Babies really, really don't need entertaining, so just do what you would normally do with DS. The mistake I made was not letting DD2 sleep in her cot when she was a bit older. In the beginning, babies sleep anywhere - they get a bit more choosy as they get bigger...so you might find that for the 1st 3 months it's easy to go and do stuff and then it gets a bit harder to get out.
Getting out takes time. Just accept it. You are looking after 2 babies. You know how to pack the changing bag, but just to remind you - nappies etc, muslin, anything you need to feed DC2, one baby book, one toy, snacks that you can both bear to eat - raisins and breadsticks last well. Don't worry about bailing out if the trip is going badly. To a 16 month old it really doesn't matter whether you actually make it to the swings/shops, but it's nice to get out.
When DS goes for his nap (does he still nap? My DD2 was so fed up of never being near her bed when she was tired, she gave up), that is your best opportunity to have a rest. Only deal with the baby if it is making fractious noises and clearly needs you. Otherwise s/he is quite happy lying on the playgym or in the cot.
Don't have a complicated 'settling the baby' routine - DS won't get it and almost certainly won't leave you to it! Take time in the first two weeks when DH is home to really get to know the baby. Watch what s/he does when s/he starts getting tired/hungry. This headed off loads of problems for me with DS (when the DDs were 4 and 2.5). DD1 was able to tell my mum 'that baby needs a sleep' when I was out. Of course, babies do just cry seemingly randomly - but, hey, it's worth trying to have some sort of clue.
We freeze dinners for the children in disposable plastic cups. So much easier to cook at a time when I have a bit of energy than leaving it to 4pm when I have my mid-afternoon slump. I also know that they eat baked beans and fish fingers and microwaved baked potatoes. I wish I had introduced them to pasta and pesto when they were younger - that looks like a proper meal.
Have in your mind what time DS needs to be ready for bed. Ours are supposed to be in pj's by 6.30pm. Then DH knows what stage people are at when he gets home - and can take over. At this point, I either collapse in a small heap on the sofa, or potter about tidying up a bit and getting grown ups dinner on.
If you need to sleep because you are so exhausted but can't, try eating an apple before hitting the coffee - it really does seem to make a difference.
At the weekend, DH takes everybody out so I can do my own thing. (That's what I'm doing now). If they are planning something really good, I go with them, but it's nice to have the choice.
Do try and make some friends, though. If someone offers help, accept it. This week, I've taken a friend's boy out for the day. Another friend offered to hoover (I had to give her a box to throw all the stuff from the carpet into so she could see what she was doing). And someone else gave the children their tea so I could go to the physio. My parents live overseas, so if I need them, I have to plan ahead - but they are very willing and able to come, and I can usually hang on with the thought that they are on their way in a few weeks.
Enjoy your children's babyhood. Take loads of photos and videos. I try never to whinge about being tired - it robs me of my joy. And I must be getting some sleep because I get woken up. One day this will all be 20 years ago, make happy memories.
Does any of that make any sense? I'm going to tidy the DDs bedroom now because it is becoming a major health hazard. Wish me luck!