I really wanted to avoid IVF and delayed it 6 months from our NHS referral, starting at age 36 after 3.5 years TTC. Once we got into it, the worst part was the emotional journey - the days after egg retrieval when you learn you have fewer and fewer embryos, waiting for calls from the clinic, are torture. The rest was unpleasant (think: you get VERY used to people shoving ultrasound wands inside you) but doable.
I don't wish I'd done it sooner, because I wanted to be really sure that this was our only real option before putting my body through it and taking on the slightly increased risks that come with an IVF pregnancy.
Be ready to do multiple rounds. Be aware of the odds for your age (I think it's around 40% per round, so it's not unusual for the first round to fail) and plan for multiple rounds. It's good to have a cut off amount of rounds in your head, e.g. 3,6 etc. You can always revisit that later if needed.
Physically, I had mild OHSS after my second round and that wasn't great, but it did pass quickly. You do get used to the injections and learn the tricks like numbing the area beforehand with ice packs.
I think my main advice is to make sure you take enough time out after egg retrieval and even during stims. Make sure your partner is lined up to support you too, there is so much information it's hard to keep track of and good if someone else can be there at appointments to take it in and sort presciptions, payment etc with you. My partner did all the injections and looked after the medication which was great.
Other things to consider:
I gained weight after my second round - doctors said this doesn't happen but 60% of people gain or lose weight, I'm pretty sure it's hormonal as my diet, lifestyle etc are identical - this meant I went into my pregnancy at a higher weight than I'd like. This wasn't major for me, tipping me just over 'normal' BMI, but maybe more of a consideration for others. NHS IVF will also want you to have a BMI under 30 in most areas before allowing you to start a round.
If you are 35 and want more than one child, consider that your eggs will never be younger than they are now. If you get pregnant after a few rounds you could easily be coming back for another child at 37/38. It may be cheaper to pay for an extra round now and bank than end up having to do 3 or 4 private rounds in 2 or 3 years. We banked 5 embryos (I'm currently pregnant so 4 left) and it has given me so much calm and emotional reassurance that I probably won't have to do the IVF process again.
The NHS aren't great at testing men. If there's any possibility sperm might not be top notch (any borderline motility or morphology results or they're talking about using ICSI), get some private testing for DNA fragmentation and a private urologist consultation. Jonathan Ramsey or Tet Yap in London are good. You will need 3 months to make any changes so do this before you start IVF if possible.
Last - depends what your NHS entitlement is but money can be a major issue. There are options for loans and funding packages if you end up doing private rounds, so it's worth exploring those early and start saving if you can.
@CMGC I had high ovarian reserve but only ended up with 2 embryos (one was aneuploid so not viable) from my first round. Unfortunately it does happen, your partner's sperm quality and that 'batch' of eggs are random each time. Had much better results on second round (10 embryos, 4 euploid). You may get a good first round though that gives you loads of embryos - I hope you do!