A shorter one may work better. 1500 I think is the next generic one down...? The spaces are more for ease of cleaning than personal aesthetics so a 1700 bath with 30mm gap at each end is a bit tight to say the least..... If you want a big bath go with a built in, that way theres no spots to collect dust and dead flies.... free standing ones do look good but they take more cleaning...

While freestanding baths are on trend you need to ensure there is enough space at the back and sides to easily reach the floor to clean both by hand and with a broom and mop. I would allow about 150mm or 6 inches on rear and each side to comfortably fit an arm. Built in baths can sit directly between walls if you get a bath with the right edge (tell the supplier if you are doing this) however they look more luxurious if there is a tile or stone surround on some or all of the bath edges. It really depends on how much space in the bathroom you can allocate for the bath. In terms of the bath size itself I would recommend a minimum of 1500mm (5ft) long but if you want to lie down go for 1700mm (about 5ft 7inches) long.

Hi Joanna We love both! A common misconception we've found with freestanding baths and spas is that they're simply be too heavy to move around for cleaning purposes. To make cleaning manageable, our 100% Australian made baths and spas are manufactured using Gelcoat composite construction which is extremely strong yet not overly heavy (5mm thickness to ensure structural rigidity and increased thermal properties). So one of our baths is typically around the 40-50kg mark which allows most people to easily slide the bath out from the wall for easy cleaning access. Freestanding stone baths are a different story altogether! Regards, Brad AQVA Luxury Baths & Spas

@bigreader i'm not a fan of built in or back to wall baths. Functionally i get why they are used but i just don't like the look of them. 
 @Ken Evers Thanks this is what i'm after some practical experience with people who have lived with this setup. As it seems to be a mixed bag, people who has said yes it's an issue but are guessing having no lived in this setup and some people who have lived with it and said not a big issue, but sometimes they are defending their choices lol. The existing bath has a drain that sits close to the wall at the same end as the shower due to the curve of the new bath this could be utilized as it would not be blocked but it would be hidden the idea was to use this as an additional drainage point with no additional plumbing. between the shower / bath section and the rest of the bathroom there will be a floor to ceiling screen approx 1000mm in length, where the current shower is that waste will also be used in addition as this will sit neatly under the floating vanity that's going in. In regards to the tiler i have used him previously and was very happy with his work, that said outside of waterproofing your right, How the water flows is a quick way to kill a good looking bathroom. The biggest concern i had was on the far side of the bath between the wall and long side. So for example against that wall? Idea is to have it slightly raise as per this photo gradient for a lineal drain. A small waste is already in this location so it was going to be used for additional drainage with something like this which is sitting under the floating vanity and in the gap between bath and wall. @Kate Yep there is some compromise we are just trying to determine how much of an issue this is for people who have actually had this layout?