Do I need a double buggy, 20 month age gap?

[giraffetales]

I'm current expecting #2 and all being well the age gap will be approximately 20 months. My mum has told me to not waste my money on a double and she did fine with my sister and I (24 month age gap) but she never went out for walks on her own or anything and I need to every day, mainly for my sanity!
I can afford it but wouldn't want to waste £1,100 either! Baby carrier is a no go ask have a dodgey back. I'm not sure about a buggy board as I've heard you have to straddle them weirdly when walking.
Any help would be much appreciated!!

I got a second hand Phil and Teds for £80 from Facebook marketplace, so definitely have a look there (it's old but perfectly functional). Unfortunately the baby cries if she's in the buggy so I normally have her in the carrier and toddler in the buggy, but it's great knowing that if I need to put her down somewhere for a few minutes, e.g. to deal with toddler tantrum or nappy change then I have a safe place to put her.

Also saying get a second hand mountain buggy - and also a second hand buggy board for your current pram